oracle if 语句中的标量子查询 PL/SQL 中的条件
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scalar subquery in if statement Condition in PL/SQL
提问by Dinesh Manne
I have an If Statement block similar to the below which is failing with the error - PLS-00103: Encountered the symbol "SELECT" when expecting one of the following....
我有一个类似于下面的 If 语句块，它因错误而失败 - PLS-00103：当期待以下之一时遇到符号“SELECT”......
Begin
If (select count(*) from Table1) > 0 then
dbms_output.put_line('Test');
end if;
end;
I have similar Case statement which works fine
我有类似的 Case 语句，它工作正常
select
case
when (select count(*) from Table1) > 0
then 2
else
1
end
from dual
From what i have read in Oracle Documentation the if and when support a Boolean Expression, any ideas whether Subqueries are supported in If Conditions.
从我在 Oracle 文档中读到的 if 和 when 支持布尔表达式，任何想法是否在 If 条件中支持子查询。
Note:The Statements have been simplified, i am not really going to get the count of the entire table, so no optimization suggestions please
注意：语句已经简化，我不是真的要得到整个表的计数，所以没有优化建议
回答by Dave Costa
No, you can't use a SELECT in the way you want.
不，您不能以您想要的方式使用 SELECT。
In your example using CASE, you are not using a CASE "statement" -- you are using a CASE expression, which happens to be embedded within a SQL statement. You can use a subquery in that case because it's within the context of a SQL statement, not a procedural statement. You wouldn't be able to use a subquery like this in a procedural CASE statement.
在您使用 CASE 的示例中，您没有使用 CASE“语句”——您使用的是 CASE表达式，它恰好嵌入在 SQL 语句中。在这种情况下，您可以使用子查询，因为它位于 SQL 语句的上下文中，而不是过程语句。您将无法在过程 CASE 语句中使用这样的子查询。
回答by u07ch
Have you called DBMS_OUTPUT.ENABLE
你有没有叫 DBMS_OUTPUT.ENABLE
Quick example
快速示例
BEGIN
DBMS_OUTPUT.DISABLE;
DBMS_OUTPUT.PUT_LINE('Disabled');
DBMS_OUTPUT.ENABLE;
DBMS_OUTPUT.PUT_LINE('Enabled');
END;
回答by cagcowboy
I don't believe subqueries are supported in IF conditions... PL/SQL will be expecting the SELECT to give it a set of records, not a single value to be used in a expression/statement.
我不相信 IF 条件支持子查询...... PL/SQL 将期望 SELECT 给它一组记录，而不是在表达式/语句中使用的单个值。
