如果(从表格中选择count(column))>然后0 [英] if (select count(column) from table) > 0 then
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问题描述
我需要检查情况.即:
if (condition)> 0 then
update table
else do not update
end if
是否需要使用select into将结果存储到变量中?
Do I need to store the result into a variable using select into?
例如:
declare valucount integer
begin
select count(column) into valuecount from table
end
if valuecount > o then
update table
else do
not update
推荐答案
您不能在PL/SQL表达式中直接使用SQL语句:
You cannot directly use a SQL statement in a PL/SQL expression:
SQL> begin
2 if (select count(*) from dual) >= 1 then
3 null;
4 end if;
5 end;
6 /
if (select count(*) from dual) >= 1 then
*
ERROR at line 2:
ORA-06550: line 2, column 6:
PLS-00103: Encountered the symbol "SELECT" when expecting one of the following:
...
...
您必须改用变量:
SQL> set serveroutput on
SQL>
SQL> declare
2 v_count number;
3 begin
4 select count(*) into v_count from dual;
5
6 if v_count >= 1 then
7 dbms_output.put_line('Pass');
8 end if;
9 end;
10 /
Pass
PL/SQL procedure successfully completed.
当然,您也许可以在SQL中完成整个工作:
Of course, you may be able to do the whole thing in SQL:
update my_table
set x = y
where (select count(*) from other_table) >= 1;
很难证明某事是不可能的.除了上面的简单测试用例之外,您还可以查看 IF
语句的语法图;您不会在任何分支中看到SELECT
语句.
It's difficult to prove that something is not possible. Other than the simple test case above, you can look at the syntax diagram for the IF
statement; you won't see a SELECT
statement in any of the branches.
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