Oracle PL/SQL:在SAMPLE子句中使用变量时出现语法错误

Question

以下PL/SQL块有效:

DECLARE
    r TABLE1%ROWTYPE;
BEGIN
    SELECT * INTO r FROM TABLE1 SAMPLE(1) WHERE ROWNUM = 1;
END;

但是,当我尝试用SAMPLE子句中的变量替换文字时,Oracle会返回语法错误:

DECLARE
    s NUMBER;
    r TABLE1%ROWTYPE;
BEGIN
    s := 1;
    SELECT * INTO r FROM TABLE1 SAMPLE(s) WHERE ROWNUM = 1;
END;

ORA-06550: line 6, column 39:
PL/SQL: ORA-00933: SQL command not properly ended

我究竟做错了什么？

我正在使用Oracle 10和SQL Developer.

(这些是简化的例子.我实际上在实践中尝试做的是优化随机行的选择,其中SAMPLE百分比将根据表中的当前行数动态计算.所以我不能使用文字,我需要一个变量来分配计算结果.)

Answer 1

所述样品synthax需要的数字.您可以使用动态SQL来构建动态查询,例如使用ref cursor:

SQL> CREATE TABLE table1 AS
  2  SELECT ROWNUM ID, rpad(ROWNUM, 10, 'x') DATA 
  3    FROM dual CONNECT BY LEVEL <= 1000;

Table created

SQL> DECLARE
  2     l_cur SYS_REFCURSOR;
  3     l_row table1%ROWTYPE;
  4     l_pct NUMBER := 50;
  5  BEGIN
  6     OPEN l_cur
  7        FOR 'SELECT * FROM table1 SAMPLE('||l_pct||') WHERE rownum = 1';
  8     LOOP
  9        FETCH l_cur INTO l_row;
 10        EXIT WHEN l_cur%NOTFOUND;
 11        dbms_output.put_line(l_row.id);
 12     END LOOP;
 13  END;
 14  /

3

PL/SQL procedure successfully completed