DB2动态表名称

Question

I want to count the rows of a number of tables. But the table name should be used dynamically. I want to do that within one SQL statement.

I tried it with

BEGIN ATOMIC 
  FOR tmp AS (
    SELECT tabschema || '.' || tabname tbl 
    FROM syscat.tables WHERE tabname LIKE '%CD') DO 
       (SELECT COUNT(*) FROM tmp.tbl); 
  END FOR; 
END

but I receive the error

DB21034E  The command was processed as an SQL statement because it was not a 
valid Command Line Processor command.  During SQL processing it returned:
SQL0204N  "TMP.TBL" is an undefined name.  LINE NUMBER=1.  SQLSTATE=42704

and found no other working solution...

Is there a solution for that? Thanks in advance.

Answer 1

I assume that your SELECT COUNT(*) FROM tmp.tbl should translate in multiple statements like

select count(*) from TABLECD
select count(*) from TABLE2CD
...

However, your query will try to do a count of the table TBL in the schema TMP.

You'll have to prepare the complete SQL statement, store it in a variable and pass it to the PREPARE statement ( documentation ).

A rather complete stored procedure which somewhat fits your requirements can be found here . The result of the counts will be stored in a table COUNTERS which you can query afterwards.

//edit: this is the example from the topic, adapt to work (not tested since I have no DB2 instance to test atm):

CREATE PROCEDURE tableCount()
LANGUAGE SQL
BEGIN
   DECLARE SQLCODE INTEGER DEFAULT 0;
   DECLARE SQLSTATE CHAR(5);
   DECLARE vTableName VARCHAR(20);
   DECLARE vTableCount INTEGER;
   DECLARE stmt varchar(2000);
   DECLARE not_found CONDITION FOR SQLSTATE '02000';
   DECLARE c1 CURSOR FOR
   SELECT tabname from syscat.tables where tabschema='DB2ADMIN';
   DECLARE C2 CURSOR FOR S2
   DECLARE CONTINUE HANDLER FOR not_found
   SET stmt = '';
   Delete from COUNTERS;
   OPEN c1;
   getRows:
   LOOP
     FETCH c1 INTO vTableName;
     IF SQLCODE = 0 THEN
       SET stmt ='SELECT Count(*) FROM ' ||  vTableName;
       PREPARE S2 FROM stmt;
       OPEN C2;
       SET vTableCount = 0;
       FETCH C2 INTO vTableCount;
       INSERT INTO COUNTERS (tableName, tableCount)
              VALUES (vTableName, vTableCount);
       CLOSE C2;
     ELSE
       LEAVE getRows;
     END IF;
   END LOOP getRows;
   CLOSE c1;
END