使用执行语句的带有索引变量的 Firebird 存储过程

Question

如何在 Firebird 存储过程中使用索引变量？我的意思是，我有输出参数 ODATE1、ODATE2、ODATE3，我可以用作 ':ODATE' || COUNTER 循环设置值？

我有 2 个这样的表：

    1. T_EMPLOYEE
    ---------------
    | ID_E | NAME |
    ---------------
    | 1    | Anne |
    ---------------
    | 2    | Bob  |
    ---------------


    2. T_WORK
    ----------------------------
    | ID_W | DATE_W     | ID_E |
    ----------------------------
    | 1    | 2021-01-01 | 1    |
    ----------------------------
    | 2    | 2021-01-01 | 2    |
    ----------------------------
    | 3    | 2021-01-02 | 1    |
    ----------------------------
    | 4    | 2021-01-03 | 2    |
    ----------------------------

我想从那个表中创建一个存储过程来得到这个结果：

    DASHBOARD
    -----------------------------------------------------------
    | OID_E | ONAME     | ODATE1     | ODATE2     | ODATE3     |
    ----------------------------------------------------------
    | 1     | Anne      |     1      |      1     |      0     |
    -----------------------------------------------------------
    | 2     | Bob       |     1      |      0     |      1     |
    -----------------------------------------------------------

我尝试在存储过程中像这样使用EXECUTE STATEMENT：

    DECLARE VARIABLE COUNTER INT;
    BEGIN

    FOR 
        SELECT ID_E, NAME FROM T_EMPLOYEE 
        INTO :OID_E, :ONAME
    D0
    BEGIN
        COUNTER = 1;
        WHILE (COUNTER<=3) DO
        BEGIN 
           EXECUTE STATEMENT 'SELECT COUNT(*) FROM T_WORK WHERE DATE_W = ''2021-01-0' || COUNTER ||
           ''' AND ID_E = ' || :OID_E || ' INTO :ODATE' || COUNTER;
    
           COUNTER = COUNTER + 1;
        END 
        SUSPEND;
    END 
    
    END  /*procedure*/

程序无法编译。 然后我尝试了这样简单的没有 COUNTER 索引替换：

    DECLARE VARIABLE COUNTER INT;
    BEGIN

    FOR 
        SELECT ID_E, NAME FROM T_EMPLOYEE 
        INTO :OID_E, :ONAME
    D0
    BEGIN
        COUNTER = 1;
        WHILE (COUNTER<=3) DO
        BEGIN 
           EXECUTE STATEMENT 'SELECT COUNT(*) FROM T_WORK WHERE ID_E = :OID_E ' ||
           ' AND DATE_W =''2021-01-02'' INTO :ODATE2';

           COUNTER = COUNTER + 1;
        END 
        SUSPEND;
    END 
    
    END  /*procedure*/

程序可以编译，但是执行时会报这个错误：

    SQL Error:  Dynamic SQL Error SQL error code = @1 Token unknown - line @1, column @2 @1. Error Code: -104. Invalid token

请给我一些见解。如何使用 EXECUTE STATEMENT 进行灵活循环来设置索引变量。 或者您有其他解决方案来满足我的需求。

附加信息：Firebird v2.5

Answer 1

您不能像这样动态引用 PSQL 变量（包括参数）。但是，您无需跳过所有这些障碍即可获得所需的结果。

你可以使用类似下面的东西（甚至不需要过程）：

select e.ID_E as OID_E, e.NAME as ONAME, 
  count(case when w.DATE_W = date '2021-01-01' then 1 end) as ODATE1,
  count(case when w.DATE_W = date '2021-01-02' then 1 end) as ODATE2,
  count(case when w.DATE_W = date '2021-01-03' then 1 end) as ODATE3
from T_EMPLOYEE e
inner join T_WORK w
  on w.ID_E = e.ID_E
group by e.ID_E, e.NAME
order by e.ID_E

小提琴：https://dbfiddle.uk/?rdbms=firebird_3.0&fiddle=59066afc0fd7f6b5cb87eac99164e899