MySQL IF 语句检查表是否为空

Question

如何创建 IF 语句，以便在发现表为空时插入默认行？我遵循这个逻辑，但有些地方是错误的。

IF ((SELECT * FROM myTable)=0)
THEN
INSERT INTO myTable
(myColumn) VALUES (myValue)
END IF;

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near

评论中的回答(McAdam331)http://sqlfiddle.com/#!9/42229/1

CREATE TABLE myTable(
  name VARCHAR(100));

INSERT INTO myTable (`name`)
SELECT 'namer'
FROM DUAL
WHERE NOT EXISTS (SELECT * FROM myTable);

Answer 1

你可以使用这样的东西:

/* Insert query */
INSERT INTO myTable (
    /* You place the values in the 'FROM' part of this query */
    SELECT tbl.*
    FROM ( SELECT 1 AS id, 'username' AS username, 'password' AS password ) AS tbl
    WHERE 0 = (SELECT COUNT(*) FROM myTable )
);

它以 INSERT 部分开头。之后是一个子查询来选择“记录”(您可以在 FROM ( SELECT ... 部分中给出值)。where 确保当前不存在记录时仅进行插入。