Question

如果发现表为空，如何创建将插入默认行的IF语句？我遵循这个逻辑，但有些不对劲。

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

回答评论（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

您可以使用以下内容：

/* 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 )
);

以INSERT部分开头。之后会出现一个子查询来选择记录＆＃39; （你可以在FROM ( SELECT ...部分给出值。如果当前没有记录，那么确保只有插入。

Answer 2

http://sqlfiddle.com/#!2/ba9ed/1

INSERT INTO table1 (myColumn)
  SELECT 
    'myValue' 
  FROM (
    SELECT COUNT(*) c 
    FROM table1 t
    HAVING c=0) t2;

用于检查表是否为空的MySQL IF语句

2 个答案: