The SQL statement in Figure 64 uses data from the Q.STAFF and Q.ORG tables to select all the clerks in the Eastern division.
If you check the sample tables in QMF sample tables, you see that the department numbers are found in both tables, the division name is in the Q.ORG table, and the job title is in the Q.STAFF table. In Q.ORG, the department number is in the DEPTNUMB column, and in Q.STAFF, the department number is in the DEPT column. You will join the tables by these two columns.
Specify all the columns you want to display on the report in the SELECT clause. Use the FROM clause to Specify the tables you want to join. Specify the columns whose values are equal in the WHERE clause, separated by an equal(=) sign.
SELECT DIVISION, ID, LOCATION, NAME FROM Q.STAFF, Q.ORG WHERE DIVISION = 'EASTERN' AND JOB='CLERK' AND DEPTNUMB = DEPT ORDER BY ID
The report in Figure 65 displays when you run the query:
DIVISION ID LOCATION NAME ---------- ------ ------------- --------- EASTERN 80 WASHINGTON JAMES EASTERN 110 BOSTON NGAN EASTERN 120 ATLANTA NAUGHTON EASTERN 170 BOSTON KERMISCH EASTERN 180 ATLANTA ABRAHAMS EASTERN 190 WASHINGTON SNEIDER
If you do not specify a common column when you join two tables, each row in the first table is joined to each row in the second table. The resulting report might contain duplicate data and might be very large.
The columns in the tables you are joining might have the same name. Use one of the following methods to distinguish between columns with the same name:
You can add a qualifier to identical column names to identify the table from which you selected the column.
For example, to distinguish between the PRODNUM column in the Q.PRODUCTS table, and the PRODNUM column in the Q.PROJECT table, add the following qualifiers to the column names:
The SQL statement in Figure 66 selects all the product numbers in both the Q.PRODUCTS and Q.PROJECT tables, the project numbers, departments, and product prices.
You only need to specify one of the duplicate column names when you select columns because the two columns are combined in the report. Use a qualifier for duplicate column names everywhere you refer to them in the query.
SELECT PROJNO, Q.PRODUCTS.PRODNUM, DEPT, PRODPRICE FROM Q.PROJECT, Q.PRODUCTS WHERE Q.PRODUCTS.PRODNUM < 100 AND Q.PRODUCTS.PRODNUM = Q.PROJECT.PRODNUM
Correlation names are used to identify the tables or views from which you selected columns when more than one column has the same name.
For example, to distinguish between the PRODNUM column in the Q.PRODUCTS table and the PRODNUM column in the Q.PROJECTS table, specify a correlation name of P for Q.PROJECT and a correlation name of S for Q.PRODUCTS.
Use the correlation name as a prefix to the column name wherever you refer to that column. The following query shows examples of using correlation names:
SELECT PROJNO, S.PRODNUM, DEPT, PRODPRICE FROM Q.PROJECT P, Q.PRODUCTS S WHERE S.PRODNUM < 100 AND S.PRODNUM = P.PRODNUM