IZ51789: SQL0901N MAY BE ISSUED EXECUTING A QUERY CONTAINING PREDICATES ON MAX OR MIN FUNCTIONS AGGREGATED ON NESTED CASE EXPRESSIONS

DB2 Version 9.1 Fix Pack 8  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 9  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 10  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 11  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 12  for Linux, UNIX and Windows

APAR status

• Closed as program error.

Error description

• SQLCODE SQL0901N may be issued while executing a query that
  satisfies the following conditions:
  - There is an equality predicate (EQPRD) in the query
  - One side of EQPRD is either a constant, host-variable or
  special register (CONST)
  - The other side of EQPRD is a column derived from the output of
  a MAX or MIN aggregate function
  - The MAX or MIN function aggregates the output of a CASE
  expression (CASEEXP)
  - CASEEXP has only 1 WHEN clause and either an ELSE NULL or no
  ELSE clause
  - The WHEN clause is also an EQPRD (WHENPRD)
  - One side WHENPRD is CONST
  - The other side WHENPRD is non-CONST
  - The THEN clause is a CASE expression (NESTCASE), i.e., nested
  inside CASEEXP
  - The THEN and ELSE clause(s) in NESTCASE do not contain
  expressions
  
  An example scenario:
  
  -- DDL
  CREATE TABLE T1 (C1 CHAR(3), C2 VARCHAR(1));
  INSERT INTO T1 VALUES ('ABC', 'A');
  INSERT INTO T1 VALUES ('BCD', 'B');
  
  -- Query
  SELECT CASE_COL_1,
         CASE_COL_2
  FROM
  (SELECT MAX(CASE WHEN C1 = 'ABC'
                  THEN (CASE WHEN C2 = ' '
                             THEN '-'
                             ELSE C2
                        END)
              END) AS CASE_COL_1,
          MIN(CASE WHEN C1 = 'BCD'
                  THEN (CASE WHEN C2 = ' '
                             THEN '-'
                             ELSE C2
                        END)
              END) AS CASE_COL_2
   FROM   T1
  ) T
  WHERE CASE_COL_1 = 'A';
  
  -- With just one such column, the -901 will be:
  SQL0901N  The SQL statement failed because of a non-severe
  system error.
  Subsequent SQL statements can be processed.  (Reason "no cast
  fcn".)
  SQLSTATE=58004
  
  -- Otherwise, it will be:
  SQL0901N The SQL statement failed because of a non-severe system
  error.
  Subsequent SQL statements can be processed. (Reason "sqlridummy:
  invalid opcode
  8 at offset <nnnn:n>".) SQLSTATE=58004
  

Local fix

• Rewrite EQPRD to a semantically equivalent
  non-relational-operator form. For the query above, this may be
  done like so:
  
  SELECT CASE_COL_1,
         CASE_COL_2
  FROM
  (SELECT MAX(CASE WHEN C1 = 'ABC'
                  THEN (CASE WHEN C2 = ' '
                             THEN '-'
                             ELSE C2
                        END)
              END) AS CASE_COL_1,
          MIN(CASE WHEN C1 = 'BCD'
                  THEN (CASE WHEN C2 = ' '
                             THEN '-'
                             ELSE C2
                        END)
              END) AS CASE_COL_2
   FROM   T1
  ) T
  WHERE CASE_COL_1 IN ('A', 'A');
  

Problem summary

• SQL0901N may be issued executing a query containing predicates
  on MAX or MIN functions aggregated on nested CASE expressions
  

Problem conclusion

• First fixed in DB2 UDB Version 9, FixPak 8
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ51788

• APAR is sysrouted TO one or more of the following:

  IC62631

Fix information

• Fixed component name

  DB2 UDB ESE SOL

• Fixed component ID

  5765F4102

Applicable component levels

• R910 PSN

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