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Druid SQL解析

2026-01-29
7 min read
后端技术
SQL解析

!!info 本篇主要学习Druid 对Sql的语法解析。学习完之后,我们可以对任意sql进行解析,同时也可以基于AST语法树来生成sql语句。 !!! 一、AST AST是abstract syntax tree的缩写，也就是抽象语法树。和所有的Parser一样，Druid Parser会生成一个抽象语法树。 在Druid中，AST节点类型主要包括SQLObject、SQLExpr、SQLSta...

!!!info 本篇主要学习Druid 对Sql的语法解析。学习完之后,我们可以对任意sql进行解析,同时也可以基于AST语法树来生成sql语句。 !!!

一、AST

AST是abstract syntax tree的缩写，也就是抽象语法树。和所有的Parser一样，Druid Parser会生成一个抽象语法树。

在Druid中，AST节点类型主要包括SQLObject、SQLExpr、SQLStatement三种抽象类型。

java

interface SQLObject {}
interface SQLExpr extends SQLObject {}
interface SQLStatement extends SQLObject {}

interface SQLTableSource extends SQLObject {}
class SQLSelect extends SQLObject {}
class SQLSelectQueryBlock extends SQLObject {}

二、语法树解析

2.1 核心类介绍

2.1.1 SQLStatemment DQL & DML顶级抽象

  • DQL 数据查询语言 select
  • DML 数据操纵语言 insert update delete

最常用的Statement当然是SELECT/UPDATE/DELETE/INSERT，他们分别是

核心类说明
SQLSelectStatement查询语句
SQLUpdateStatement更新语句
SQLDeleteStatement删除语句
SQLInsertStatement新增语句
java
@Test
public void statement() {
    // 以下全部 true
    System.out.println(SQLUtils.parseSingleMysqlStatement("select * from users") instanceof SQLSelectStatement);
System.out.println(SQLUtils.parseSingleMysqlStatement("insert into users(id,name,age) values (1,'孙悟空',500)") instanceof SQLInsertStatement);
System.out.println(SQLUtils.parseSingleMysqlStatement("update users set name = '唐僧' where id = 1 ") instanceof SQLUpdateStatement);
System.out.println(SQLUtils.parseSingleMysqlStatement("delete from users where id = 1") instanceof SQLDeleteStatement);
}

2.1.2 SQLSelect SQL查询

SQLSelectStatement包含一个SQLSelect，SQLSelect包含一个SQLSelectQuery。SQLSelectQuery有主要的两个派生类， 分别是SQLSelectQueryBlock(单表sql查询)和SQLUnionQuery(union查询)。

java
    /**
     * SQLSelectStatement包含一个SQLSelect，SQLSelect包含一个SQLSelectQuery。SQLSelectQuery有主要的两个派生类，
     * 分别是SQLSelectQueryBlock(单表sql查询)和SQLUnionQuery(联合查询)。
     */
    @Test
    public void SQLSelectQuery() {
        // true
        System.out.println(parseSQLSelectQuery("select * from users") instanceof SQLSelectQueryBlock);
// true
        System.out.println(parseSQLSelectQuery("select name from users union select name from school") instanceof SQLUnionQuery);
}

    public SQLSelectQuery parseSQLSelectQuery(String sql) {
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement(sql);
SQLSelectStatement sqlSelectStatement = Utils.cast(sqlStatement, SQLSelectStatement.class);
SQLSelect select = sqlSelectStatement.getSelect();
return select.getQuery();
}

2.1.3 SQLExpr

SQLExpr 是有几个实现类的。

sql
select id,name,age from users where id = 1 and name = '孙悟空';

select u.id, u.name from users as u where id = 1 and name = ?;
核心类举例说明适用范围快速记忆
SQLIdentifierExprid,name,ageSQLIdentifierExpr查询字段或者where条件唯一标记
SQLPropertyExpru.id,u.name区别于SQLIdentifierExpr,适用于有别名的场景; SQLPropertyExpr.name = id, SQLPropertyExpr.owner = SQLIdentifierExpr = u）查询字段或者where条件有别名就是它
SQLBinaryOpExprid = 1, id > 5SQLBinaryOpExpr(left = SQLIdentifierExpr = id ,right = SQLValuableExpr = 1)where条件有操作符就是它
SQLVariantRefExprid = ?变量where条件有变量符就是它
SQLIntegerExprid = 1数字类型值类型-
SQLCharExprname = '孙悟空'字符类型值类型-

2.1.3.1 SQLBinaryOpExpr

java
    /**
     * 操作符相关: SQLBinaryOpExpr
     */
    @Test
    public void SQLBinaryOpExpr() {
        String sql = "select * from users where id > 1 and age = 18";
SQLSelectQuery sqlSelectQuery = Utils.parseSQLSelectQuery(sql);
SQLSelectQueryBlock selectQueryBlock = Utils.cast(sqlSelectQuery, SQLSelectQueryBlock.class);
SQLExpr where = selectQueryBlock.getWhere();
List<SQLObject> conditions = where.getChildren();
// [id > 1 , age = 18] 出现了操作符所以是SQLBinaryOpExpr
        for (SQLObject condition : conditions) {
            SQLBinaryOpExpr conditionExpr = Utils.cast(condition, SQLBinaryOpExpr.class);
SQLBinaryOperator operator = conditionExpr.getOperator();
SQLIdentifierExpr conditionColumn = Utils.cast(conditionExpr.getLeft(), SQLIdentifierExpr.class);
SQLValuableExpr conditionColumnValue = Utils.cast(conditionExpr.getRight(), SQLValuableExpr.class);
Utils.print("条件字段:{},操作符号:{},条件值:{}", conditionColumn.getName(), operator.name, conditionColumnValue);
}
    }

2.1.3.2 SQLVariantRefExpr

java
    @Test
    public void SQLVariantRefExpr() {
        String sql = "select * from users where id = ? and name = ?";
SQLSelectQuery sqlSelectQuery = Utils.parseSQLSelectQuery(sql);
SQLSelectQueryBlock selectQueryBlock = Utils.cast(sqlSelectQuery, SQLSelectQueryBlock.class);
SQLExpr where = selectQueryBlock.getWhere();
List<SQLObject> conditions = where.getChildren();
// [id = ?] 出现了变量符,所以要用SQLVariantRefExpr
        for (SQLObject condition : conditions) {
            SQLBinaryOpExpr conditionExpr = Utils.cast(condition, SQLBinaryOpExpr.class);
SQLBinaryOperator operator = conditionExpr.getOperator();
SQLIdentifierExpr conditionColumn = Utils.cast(conditionExpr.getLeft(), SQLIdentifierExpr.class);
SQLVariantRefExpr conditionColumnValue = Utils.cast(conditionExpr.getRight(), SQLVariantRefExpr.class);
int index = conditionColumnValue.getIndex();
Utils.print("条件字段:{},操作符号:{},索引位:{}", conditionColumn.getName(), operator.name, index);
}
    }

2.1.4 SQLTableSource

常见的SQLTableSource包括SQLExprTableSource、SQLJoinTableSource、SQLSubqueryTableSource、SQLWithSubqueryClause.Entry

|核心类|举例|说明|快速记忆| |:--|:--|:--|:--|:--| |SQLExprTableSource|select * from emp where i = 3| name = SQLIdentifierExpr = emp| 单表查询 | |SQLJoinTableSource|select * from emp e inner join org o on e.org_id = o.id| left = SQLExprTableSource(emp e),right = SQLExprTableSource(org o), condition = SQLBinaryOpExpr(e.org_id = o.id) | join 查询使用 | |SQLSubqueryTableSource|select * from (select * from temp) a|from(...)是一个SQLSubqueryTableSource|子查询语句| |SQLWithSubqueryClause| WITH RECURSIVE ancestors AS (SELECT * FROM org UNION SELECT f.* FROM org f, ancestors a WHERE f.id = a.parent_id ) SELECT * FROM ancestors; |ancestors AS (...) 是一个SQLWithSubqueryClause.Entry|with|

2.2 SQL语句解析示例

2.2.1 解析 Where

注意如果条件语句中只有一个条件,那么where就是一个 SQLBinaryOpExpr。 当条件大于2个,使用 where.getChildren()

java
    /**
     * 判断where要
     * 1. 注意是SQLBinaryOpExpr(id = 1) or (u.id = 1) 需要注意是否使用了别名<br>
     * 2. 注意如果只有一个查询添加 where本身就是一个SQLBinaryOpExpr，如果是多个就要用 where.getChildren()<br></>
     * 如果有别名: SQLPropertyExpr(name = id , ownerName = u)<br>
     * 如果没别名: SQLIdentifierExpr(name = id) <br></>
     * 值对象: SQLValuableExpr
     *
     * @param where 条件对象
     */
    public static void parseWhere(SQLExpr where) {
        if (where instanceof SQLBinaryOpExpr) {
            parseSQLBinaryOpExpr(cast(where, SQLBinaryOpExpr.class));
} else {
            List<SQLObject> childrenList = where.getChildren();
for (SQLObject sqlObject : childrenList) {
                // 包含了 left 和 right
                SQLBinaryOpExpr conditionBinary = cast(sqlObject, SQLBinaryOpExpr.class);
parseSQLBinaryOpExpr(conditionBinary);
}
        }

    }

     public static void parseSQLBinaryOpExpr(SQLBinaryOpExpr conditionBinary) {
        SQLExpr conditionExpr = conditionBinary.getLeft();
SQLExpr conditionValueExpr = conditionBinary.getRight();
// 左边有别名所以是SQLPropertyExpr
        if (conditionExpr instanceof SQLPropertyExpr) {
            SQLPropertyExpr conditionColumnExpr = cast(conditionExpr, SQLPropertyExpr.class);
// 右边根据类型进行转换 id是SQLIntegerExpr name是SQLCharExpr
            SQLValuableExpr conditionColumnValue = cast(conditionValueExpr, SQLValuableExpr.class);
print("条件列名:{},条件别名:{},条件值:{}", conditionColumnExpr.getName(), conditionColumnExpr.getOwnernName(), conditionColumnValue);
}
        // 如果没有别名
        if (conditionExpr instanceof SQLIdentifierExpr) {
            SQLIdentifierExpr conditionColumnExpr = cast(conditionExpr, SQLIdentifierExpr.class);
SQLValuableExpr conditionColumnValue = cast(conditionValueExpr, SQLValuableExpr.class);
print("条件列名:{},条件值:{}", conditionColumnExpr.getName(), conditionColumnValue);
}
    }

2.2.2 解析 SQLSelectItem

解析查询的列信息

java
    /**
     * 解析查询字段,注意是否使用了别名.u.id as userId, u.name as userName, u.age as userAge<br>
     * userId（sqlSelectItem.getAlias）<br>
     * 如果有别名: u.id( id = SQLPropertyExpr.getName,u = SQLPropertyExpr.getOwnernName)<br>
     * 如果没别名: id(id = SQLIdentifierExpr.name)
     *
     * @param selectColumnList 查询字段
     */
    private void parseSQLSelectItem(List<SQLSelectItem> selectColumnList) {
        for (SQLSelectItem sqlSelectItem : selectColumnList) {
            // u.id as userId(selectColumnAlias)
            String selectColumnAlias = sqlSelectItem.getAlias();
// u.id = SQLPropertyExpr
            SQLExpr expr = sqlSelectItem.getExpr();
if (expr instanceof SQLPropertyExpr) {
                SQLPropertyExpr selectColumnExpr = cast(expr, SQLPropertyExpr.class);
print("列名:{},别名:{},表别名:{}", selectColumnExpr.getName(), selectColumnAlias, selectColumnExpr.getOwnernName());
}
            if (expr instanceof SQLIdentifierExpr) {
                SQLIdentifierExpr selectColumnExpr = cast(expr, SQLIdentifierExpr.class);
print("列名:{},别名:{}", selectColumnExpr.getName(), selectColumnAlias);
}
        }
    }

2.2.3 解析 SQLUpdateSetItem

java
    @Test
    public void SQLUpdateStatement() {
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement("update users u set u.name = '唐僧',age = 18 where u.id = 1 ");
SQLUpdateStatement sqlUpdateStatement = Utils.cast(sqlStatement, SQLUpdateStatement.class);
List<SQLUpdateSetItem> setItems = sqlUpdateStatement.getItems();
for (SQLUpdateSetItem setItem : setItems) {
            SQLExpr column = setItem.getColumn();
if (column instanceof SQLPropertyExpr) {
                SQLPropertyExpr sqlPropertyExpr = Utils.cast(column, SQLPropertyExpr.class);
SQLExpr value = setItem.getValue();
Utils.print("column:{},列owner:{},value:{}", sqlPropertyExpr.getName(), sqlPropertyExpr.getOwnernName(), value);
}
            if (column instanceof SQLIdentifierExpr) {
                SQLExpr value = setItem.getValue();
Utils.print("column:{},value:{}", column, value);
}
        }
        SQLExpr where = sqlUpdateStatement.getWhere();
Utils.startParse("解析where", Utils::parseWhere, where);
}

2.2.4 解析 SQLLimit

java
    /**
     * 偏移量,只有2个值
     *
     * @param limit 限制
     */
    private void parseLimit(SQLLimit limit) {
        // 偏移量
        SQLExpr offset = limit.getOffset();
// 便宜数量
        SQLExpr rowCount = limit.getRowCount();
print("偏移量:{},偏移数量:{}", offset, rowCount);
}

2.2.5 解析 SQLSelectGroupBy

java
    @Test
    public void groupBy() {
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement("select name,count(1) as count from users group by name,age having count > 2");
SQLSelectStatement selectStatement = Utils.cast(sqlStatement, SQLSelectStatement.class);
SQLSelect select = selectStatement.getSelect();
SQLSelectQueryBlock query = Utils.cast(select.getQuery(), SQLSelectQueryBlock.class);
SQLSelectGroupByClause groupBy = query.getGroupBy();
List<SQLExpr> items = groupBy.getItems();
for (SQLExpr item : items) {
            // group by name
            // group by age
            SQLIdentifierExpr groupByColumn = Utils.cast(item, SQLIdentifierExpr.class);
Utils.print("group by {}", groupByColumn);
}
    }

2.2.6 解析 Having

java
    @Test
    public void having() {
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement("select name,count(1) as count from users group by name,age having count > 2");
SQLSelectStatement selectStatement = Utils.cast(sqlStatement, SQLSelectStatement.class);
SQLSelect select = selectStatement.getSelect();
SQLSelectQueryBlock query = Utils.cast(select.getQuery(), SQLSelectQueryBlock.class);
SQLSelectGroupByClause groupBy = query.getGroupBy();
SQLExpr having = groupBy.getHaving();
// 因为只有一个条件,所以having就是SQLBinaryOpExpr
        SQLBinaryOpExpr havingExpr = Utils.cast(having, SQLBinaryOpExpr.class);
// 没有使用别名,所以就是SQLIdentifierExpr
        SQLExpr left = havingExpr.getLeft();
SQLIdentifierExpr leftExpr = Utils.cast(left, SQLIdentifierExpr.class);
// 数字类型就是
        SQLExpr right = havingExpr.getRight();
SQLValuableExpr rightValue = Utils.cast(right, SQLValuableExpr.class);
SQLBinaryOperator operator = havingExpr.getOperator();
// left:count, operator:>,right:2
        Utils.print("left:{}, operator:{},right:{}", leftExpr.getName(), operator.name, rightValue.getValue());
}

三、语法树生成

前面的内容如果都搞清楚了,那么我们就能对sql进行解析,通知可以修改sql解析后的语法树,同时再将修改后的语法树,重新转换成sql

3.1 修改语法树

3.1.1 增加一个条件

java
    @Test
    public void SQLDeleteStatement(){
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement("delete from users where id = 1");
SQLDeleteStatement sqlDeleteStatement = Utils.cast(sqlStatement, SQLDeleteStatement.class);
sqlDeleteStatement.addCondition(SQLUtils.toSQLExpr("name = '孙悟空'"));
//        DELETE FROM users
    //        WHERE id = 1
              //        AND name = '孙悟空'
              System.out.println(SQLUtils.toSQLString(sqlDeleteStatement));
}

3.1.2 修改一个条件值

将条件id = 1 修改成 id = 2

java
    @Test
    public void SQLDeleteStatement2(){
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement("delete from users where id = 1");
SQLDeleteStatement sqlDeleteStatement = Utils.cast(sqlStatement, SQLDeleteStatement.class);
SQLExpr where = sqlDeleteStatement.getWhere();
SQLBinaryOpExpr sqlBinaryOpExpr = Utils.cast(where, SQLBinaryOpExpr.class);
//        DELETE FROM users
    //        WHERE id = 2
              sqlBinaryOpExpr.setRight(SQLUtils.toSQLExpr("2"));
System.out.println(SQLUtils.toSQLString(sqlDeleteStatement));
}

四、Visitor模式

访问者模式

所有的AST节点都支持Visitor模式，需要自定义遍历逻辑，可以实现相应的ASTVisitorAdapter派生类

java
    public static class CustomerMySqlASTVisitorAdapter extends MySqlASTVisitorAdapter {

        private final Map<String, SQLTableSource> ALIAS_MAP = new HashMap<String, SQLTableSource>();

private final Map<String, SQLExpr> ALIAS_COLUMN_MAP = new HashMap<String, SQLExpr>();


public boolean visit(SQLExprTableSource x) {
            String alias = x.getAlias();
ALIAS_MAP.put(alias, x);
return true;
}

        @Override
        public boolean visit(MySqlSelectQueryBlock x) {
            List<SQLSelectItem> selectList = x.getSelectList();
for (SQLSelectItem sqlSelectItem : selectList) {
                String alias = sqlSelectItem.getAlias();
SQLExpr expr = sqlSelectItem.getExpr();
ALIAS_COLUMN_MAP.put(alias, expr);
}
            return true;
}

        public Map<String, SQLTableSource> getAliasMap() {
            return ALIAS_MAP;
}

        public Map<String, SQLExpr> getAliasColumnMap() {
            return ALIAS_COLUMN_MAP;
}
    }

    @Test
    public void AliasVisitor() {
        String sql = "select u.id as userId, u.name as userName, age as userAge from users as u where u.id = 1 and u.name = '孙悟空' limit 2,10";
// 解析SQL
        SQLStatement sqlStatement = SQLUtils.parseSingleMysqlStatement(sql);
CustomerMySqlASTVisitorAdapter customerMySqlASTVisitorAdapter = new CustomerMySqlASTVisitorAdapter();
sqlStatement.accept(customerMySqlASTVisitorAdapter);
// 表别名:{u=users}
        System.out.println("表别名:" + customerMySqlASTVisitorAdapter.getAliasMap());
// 列别名{userName=u.name, userId=u.id, userAge=age}
        System.out.println("列别名" + customerMySqlASTVisitorAdapter.getAliasColumnMap());
}
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最后更新于 2026-01-29
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