问题描述
如何在 MySQL 存储过程中构建和使用动态 sql?
How do you build and use dynamic sql in a MySQL stored procedure?
推荐答案
我不相信 MySQL 支持动态 sql.你可以做准备"类似但不同的陈述.
I don't believe MySQL supports dynamic sql. You can do "prepared" statements which is similar, but different.
这是一个例子:
mysql> PREPARE stmt FROM
-> 'select count(*)
-> from information_schema.schemata
-> where schema_name = ? or schema_name = ?'
;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> EXECUTE stmt
-> USING @schema1,@schema2
+----------+
| count(*) |
+----------+
| 2 |
+----------+
1 row in set (0.00 sec)
mysql> DEALLOCATE PREPARE stmt;
准备好的语句通常用于查看给定查询的执行计划.由于它们是使用 execute 命令执行的，并且可以将 sql 分配给一个变量，因此您可以近似一些与动态 sql 相同的行为.
The prepared statements are often used to see an execution plan for a given query. Since they are executed with the execute command and the sql can be assigned to a variable you can approximate the some of the same behavior as dynamic sql.
这是一个很好的链接 关于这个:
Here is a good link about this:
不要忘记使用最后一行解除分配stmt！
Don't forget to deallocate the stmt using the last line!
祝你好运！
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