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]
With other database servers than Informix, when the subscript notation is used to modify column values in UPDATE statement, or as ORDER BY element, you will get and SQL error:
UPDATE tab1 SET col1[2,3] = 'RO' WHERE ...
SELECT ... FROM tab1 ORDER BY col1[1,3]
Informix SQL provides a various set of substring functions:
  • SUBSTR( str-expr, start-pos [, length ] )
  • SUBSTRB( str-expr, start-pos [, length ] )
  • SUBSTRING( str-expr FROM start-pos [FOR length ] )
  • SUBSTRING_INDEX( str-expr, delimiter, count )


Netezza provides the SUBSTRING( ... from ... to ... ) function, to extract a substring from a string expression:

SELECT .... FROM tab1 WHERE SUBSTRING(col1 from 2 for 2) = 'RO'
SELECT SUBSTRING('Some text' from 6 for 3) ... -- Gives 'tex'


Replace all Informix col[x,y] right-value expressions by SUBSTRING( col from x for (y-x+1) ).

Rewrite UPDATE and ORDER BY clauses using col[x,y] expressions.

The Informix substring functions SUBSTR(), SUBSTRB(), SUBSTRING() and SUBSTRING_INDEX() are not converted by the ODI driver.

The translation of col[x,y] expressions can be controlled with the following FGLPROFILE entry:
dbi.database.dsname.ifxemul.colsubs = { true | false }
For more details see IBM Informix emulation parameters in FGLPROFILE.