Substrings in SQL

Informix® SQL statements can use subscripts on columns defined with the character data type:

SELECT ... FROM tab1 WHERE col1[2,3] = 'RO'
SELECT ... FROM tab1 WHERE col1[10] = 'R'   -- Same as col1[10,10]
UPDATE tab1 SET col1[2,3] = 'RO' WHERE ...
SELECT ... FROM tab1 ORDER BY col1[1,3] 

While IBM® DB2® provides the SUBSTR() function, to extract a substring from a string expression:

SELECT .... FROM tab1 WHERE SUBSTR(col1,2,2) = 'RO'
SELECT SUBSTR('Some text',6,3)FROM DUAL -- Gives 'tex' 

Solution

You must replace all Informix col[x,y] expressions by SUBSTR(col,x,y-x+1).

Important:
  • In UPDATE instructions, setting column values through subscripts will produce an error with IBM DB2:

    UPDATE tab1 SET col1[2,3] = 'RO' WHERE ...

    is converted to:

    UPDATE tab1 SET SUBSTR(col1,2,3-2+1) = 'RO' WHERE ...

  • Column subscripts in ORDER BY expressions produce an error with IBM DB2:

    SELECT ... FROM tab1 ORDER BY col1[1,3]

    is converted to:

    SELECT ... FROM tab1 ORDER BY SUBSTR(col1,1,3-1+1)