如何记录是否存在，如何不插入 [英] How to check if record exists, if not insert

问题描述

我正在建立一个博客网站，我需要在将标签插入tblTag之前检查标签是否存在

I'm making a blog site and I need to check if a tag exists before inserting the tag into the tblTag

这就是我正在尝试的：

 $var_sqlTagsCheck = "IF (EXISTS(SELECT * FROM tblTag t WHERE t.tagName = '$var_tagCollectInsert'))
 BEGIN
    INSERT IGNORE INTO tblTag
 SET tagName = '$var_tagCollectInsert'
 END
 ELSE
 BEGIN
 INSERT INTO tblTag (tagId, tagName) VALUES ('', '$var_tagCollectInsert'))
 END
 ";

但是工作不正常，有人可以借给我一些帮助吗？哪里出错了，这似乎是相当直接的SQL。

But is not working correctly, can anybody lend me some assistance here?? Where am i going wrong, this seems fairly straight forward SQL.

推荐答案

尝试使用 EXISTS 谓词在 WHERE 子句中：

Try using the EXISTS predicate in the WHERE clause:

 INSERT INTO tblTag (tagId, tagName)
 SELECT '', '$var_tagCollectInsert'
 WHERE NOT EXISTS(SELECT * FROM tblTag t
                  WHERE t.tagName = '$var_tagCollectInsert'));

MySQL的 INSERT INTO 的一般形式是：

The general form of MySQL's INSERT INTO is:

INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE]
    [INTO] tbl_name [(col_name,...)]
    SELECT ...
    [ ON DUPLICATE KEY UPDATE
      col_name=expr
        [, col_name=expr] ... ]

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