如何在没有 UNION 或 UNION ALL 的情况下组合多个 SQL 查询？

Question

There are 4 SELECT queries with JOIN consisting of different number of columns

• Table A1- 6 columns
• Table A2 - 11 columns
• Table A3 - 3 columns
• Table A4 - 3 columns

Sample sql query of mine:

SELECT * FROM Table A1 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT * FROM Table A2 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT * FROM Table A3 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT * FROM Table A4 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A';

This above query is returning error like this, ofcourse because there are mismatch in number of columns.

ORA-01789: query block has incorrect number of result columns 01789. 00000 - "query block has incorrect number of result columns"

Please let me know any ways to do without using UNION or UNION ALL.

Answer 1

You need to write column names, if one of the tables does not contain any of field that the field exists on another table you can use custom columns.

Let's say that fieldC does not exist on TableA4;

SELECT fieldA, fieldB, fieldC FROM Table A1 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, fieldC FROM Table A2 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, fieldC FROM Table A3 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, NULL as fieldC FROM Table A4 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A';

We can also rename fields, but in this case we must be very careful about type and data compatibility;

SELECT someFieldA as fieldA, someFieldB as fieldB, someFieldC as fieldC FROM Table A1 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, fieldC FROM Table A2 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, fieldC FROM Table A3 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A'
UNION ALL
SELECT fieldA, fieldB, NULL as fieldC FROM Table A4 INNER JOIN table B ON B.fieldnaame = 'ABC' AND fieldname = 'A';