mysql - 这里有文本到数字的转换吗？

Question

我有一个表，其中有一列amounttype DEC。
以下查询有效：
SELECT * FROM mytable WHERE amount < '1';

SELECT * FROM mytable WHERE amount = '1.5';

即即使我使用引号之类的amount字符值（尽管它们实际是数字），查询仍然有效。

我的问题是：
这是因为SQL Server“理解”数据类型实际上是数字并在执行sql时忽略引号select
还是
SQL Server首先将amount值转换为文本然后进行比较？所以这有一个性能转换导致的开销？

score -1 · Accepted Answer

Yes there is a numerical conversion happening, since the column 'amount' is defined as numerical. To test this, you can try:

SELECT * FROM mytable WHERE amount < '1a';

you will get the error message:

Msg 8114, Level 16, State 5, Line 1
Error converting data type varchar to numeric.

meaning that varchar is being converted to numeric and not the other way round.

1 回答 1