动态拼字符串，嵌套if else

[Jenf_Mu]

declare @v;

EXEC(
'select top '
+
(if  @v = 1 '1' else '10')
+
' * from appointment'
)

想根据变量值的不同，拼出不同的SQL

[卖水果的net]

1、if 语句，你要换成 case when 2、把动态语句，在 exec 之前，先拼接完成

[Jenf_Mu]

int QSqlQuery::size() const

Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes. Note that for non-SELECT statements (isSelect() returns false), size() will return -1. If the query is not active (isActive() returns false), -1 is returned.

数据库不支持返回行数，Qt也没办法。 建议用next()遍历数据集。 如果实在想知道多少行，那就查count呗。

[Jenf_Mu]

回错贴了，抱歉

引用 2 楼 Jenf_Mu 的回复:

int QSqlQuery::size() const

Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes. Note that for non-SELECT statements (isSelect() returns false), size() will return -1. If the query is not active (isActive() returns false), -1 is returned.

数据库不支持返回行数，Qt也没办法。 建议用next()遍历数据集。 如果实在想知道多少行，那就查count呗。

[中国风]

改为 e.g.

declare @v INT,@sql VARCHAR(max);
 
 SET @sql='select top '
+
(CASE WHEN   @v = 1 THEN '1' else '10' END)
+
' * from appointment'
EXEC(
@sql
)