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341 lines
8.5 KiB
Markdown
341 lines
8.5 KiB
Markdown
---
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layout: post
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title: SQL 拼接
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tags: sql database Java
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categories: database
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published: true
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---
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在java中进行SQL拼接是一件无比痛苦的工作，这是由于需要通过判断参数动态生成SQL
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而且拼接时产生满屏幕的加号或者append，使SQL几乎失去了可读性，那么丢失`WHERE`，`AND`，逗号等语法错误将随之而来
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最近研究mybatis时发现了一个非常好用的工具类 SQL Builder [^sqlBuilder]
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## 示例
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~~~java
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@Test
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public void test(){
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String sql = new SQL(){ {
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SELECT("name");
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SELECT("password");
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SELECT("sex");
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FROM("student s");
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INNER_JOIN("info i on s.id = i.id");
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WHERE(String.format("name = '%s'","HanMeiMei"));
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} }.toString();
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System.out.println(sql);
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}
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~~~
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运行结果为：
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SELECT name, password, sex
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FROM student s
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INNER JOIN info i on s.id = i.id
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WHERE (name = 'HanMeiMei' AND i.sex = 1)
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SQL的拼接词都自动生成了
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## 源码
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事实上不必为了使用这个类而引入Mybatis，SQL Builder非常简单，简单到没有使用任何第三方类库，只需将这个类复制粘贴一下就可以直接用了。
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SQL Builder 全部代码
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~~~java
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.List;
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public abstract class AbstractSQL<T> {
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private static final String AND = ") \nAND (";
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private static final String OR = ") \nOR (";
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public abstract T getSelf();
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public T UPDATE(String table) {
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sql().statementType = SQLStatement.StatementType.UPDATE;
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sql().tables.add(table);
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return getSelf();
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}
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public T SET(String sets) {
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sql().sets.add(sets);
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return getSelf();
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}
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public T INSERT_INTO(String tableName) {
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sql().statementType = SQLStatement.StatementType.INSERT;
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sql().tables.add(tableName);
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return getSelf();
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}
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public T VALUES(String columns, String values) {
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sql().columns.add(columns);
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sql().values.add(values);
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return getSelf();
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}
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public T SELECT(String columns) {
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sql().statementType = SQLStatement.StatementType.SELECT;
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sql().select.add(columns);
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return getSelf();
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}
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public T SELECT_DISTINCT(String columns) {
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sql().distinct = true;
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SELECT(columns);
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return getSelf();
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}
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public T DELETE_FROM(String table) {
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sql().statementType = SQLStatement.StatementType.DELETE;
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sql().tables.add(table);
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return getSelf();
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}
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public T FROM(String table) {
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sql().tables.add(table);
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return getSelf();
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}
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public T JOIN(String join) {
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sql().join.add(join);
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return getSelf();
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}
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public T INNER_JOIN(String join) {
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sql().innerJoin.add(join);
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return getSelf();
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}
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public T LEFT_OUTER_JOIN(String join) {
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sql().leftOuterJoin.add(join);
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return getSelf();
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}
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public T RIGHT_OUTER_JOIN(String join) {
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sql().rightOuterJoin.add(join);
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return getSelf();
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}
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public T OUTER_JOIN(String join) {
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sql().outerJoin.add(join);
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return getSelf();
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}
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public T WHERE(String conditions) {
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sql().where.add(conditions);
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sql().lastList = sql().where;
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return getSelf();
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}
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public T OR() {
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sql().lastList.add(OR);
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return getSelf();
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}
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public T AND() {
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sql().lastList.add(AND);
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return getSelf();
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}
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public T GROUP_BY(String columns) {
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sql().groupBy.add(columns);
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return getSelf();
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}
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public T HAVING(String conditions) {
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sql().having.add(conditions);
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sql().lastList = sql().having;
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return getSelf();
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}
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public T ORDER_BY(String columns) {
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sql().orderBy.add(columns);
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return getSelf();
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}
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private SQLStatement sql = new SQLStatement();
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private SQLStatement sql() {
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return sql;
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}
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public <A extends Appendable> A usingAppender(A a) {
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sql().sql(a);
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return a;
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}
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@Override
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public String toString() {
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StringBuilder sb = new StringBuilder();
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sql().sql(sb);
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return sb.toString();
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}
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private static class SafeAppendable {
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private final Appendable a;
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private boolean empty = true;
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public SafeAppendable(Appendable a) {
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super();
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this.a = a;
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}
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public SafeAppendable append(CharSequence s) {
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try {
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if (empty && s.length() > 0) empty = false;
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a.append(s);
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} catch (IOException e) {
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throw new RuntimeException(e);
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}
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return this;
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}
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public boolean isEmpty() {
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return empty;
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}
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}
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private static class SQLStatement {
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public enum StatementType {
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DELETE, INSERT, SELECT, UPDATE
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}
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StatementType statementType;
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List<String> sets = new ArrayList<String>();
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List<String> select = new ArrayList<String>();
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List<String> tables = new ArrayList<String>();
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List<String> join = new ArrayList<String>();
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List<String> innerJoin = new ArrayList<String>();
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List<String> outerJoin = new ArrayList<String>();
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List<String> leftOuterJoin = new ArrayList<String>();
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List<String> rightOuterJoin = new ArrayList<String>();
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List<String> where = new ArrayList<String>();
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List<String> having = new ArrayList<String>();
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List<String> groupBy = new ArrayList<String>();
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List<String> orderBy = new ArrayList<String>();
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List<String> lastList = new ArrayList<String>();
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List<String> columns = new ArrayList<String>();
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List<String> values = new ArrayList<String>();
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boolean distinct;
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private void sqlClause(SafeAppendable builder, String keyword, List<String> parts, String open, String close,
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String conjunction) {
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if (!parts.isEmpty()) {
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if (!builder.isEmpty())
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builder.append("\n");
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builder.append(keyword);
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builder.append(" ");
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builder.append(open);
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String last = "________";
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for (int i = 0, n = parts.size(); i < n; i++) {
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String part = parts.get(i);
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if (i > 0 && !part.equals(AND) && !part.equals(OR) && !last.equals(AND) && !last.equals(OR)) {
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builder.append(conjunction);
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}
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builder.append(part);
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last = part;
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}
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builder.append(close);
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}
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}
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private String selectSQL(SafeAppendable builder) {
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if (distinct) {
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sqlClause(builder, "SELECT DISTINCT", select, "", "", ", ");
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} else {
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sqlClause(builder, "SELECT", select, "", "", ", ");
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}
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sqlClause(builder, "FROM", tables, "", "", ", ");
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sqlClause(builder, "JOIN", join, "", "", "\nJOIN ");
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sqlClause(builder, "INNER JOIN", innerJoin, "", "", "\nINNER JOIN ");
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sqlClause(builder, "OUTER JOIN", outerJoin, "", "", "\nOUTER JOIN ");
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sqlClause(builder, "LEFT OUTER JOIN", leftOuterJoin, "", "", "\nLEFT OUTER JOIN ");
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sqlClause(builder, "RIGHT OUTER JOIN", rightOuterJoin, "", "", "\nRIGHT OUTER JOIN ");
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sqlClause(builder, "WHERE", where, "(", ")", " AND ");
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sqlClause(builder, "GROUP BY", groupBy, "", "", ", ");
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sqlClause(builder, "HAVING", having, "(", ")", " AND ");
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sqlClause(builder, "ORDER BY", orderBy, "", "", ", ");
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return builder.toString();
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}
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private String insertSQL(SafeAppendable builder) {
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sqlClause(builder, "INSERT INTO", tables, "", "", "");
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sqlClause(builder, "", columns, "(", ")", ", ");
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sqlClause(builder, "VALUES", values, "(", ")", ", ");
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return builder.toString();
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}
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private String deleteSQL(SafeAppendable builder) {
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sqlClause(builder, "DELETE FROM", tables, "", "", "");
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sqlClause(builder, "WHERE", where, "(", ")", " AND ");
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return builder.toString();
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}
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private String updateSQL(SafeAppendable builder) {
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sqlClause(builder, "UPDATE", tables, "", "", "");
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sqlClause(builder, "SET", sets, "", "", ", ");
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sqlClause(builder, "WHERE", where, "(", ")", " AND ");
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return builder.toString();
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}
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public String sql(Appendable a) {
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SafeAppendable builder = new SafeAppendable(a);
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if (statementType == null) {
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return null;
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}
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String answer;
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switch (statementType) {
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case DELETE:
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answer = deleteSQL(builder);
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break;
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case INSERT:
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answer = insertSQL(builder);
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break;
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case SELECT:
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answer = selectSQL(builder);
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break;
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case UPDATE:
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answer = updateSQL(builder);
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break;
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default:
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answer = null;
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}
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return answer;
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}
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}
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}
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public class SQL extends AbstractSQL<SQL> {
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@Override
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public SQL getSelf() {
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return this;
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}
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}
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~~~
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[^sqlBuilder]: [http://mybatis.github.io/mybatis-3/statement-builders.html](http://mybatis.github.io/mybatis-3/statement-builders.html) |