ASA SQL Reference
  SQL Language Elements
    Operators

String operators

expression || expression    String concatenation (two vertical bars). If either string is NULL, it is treated as the empty string for concatenation.

expression + expression    Alternative string concatenation. When using the + concatenation operator, you must ensure the operands are explicitly set to character data types rather than relying on implicit data conversion.

For example, the following query returns the integer value 579:

SELECT 123 + 456

whereas the following query returns the character string 123456:

SELECT '123' + '456'

You can use the CAST or CONVERT function to explicitly convert data types.

Standards and compatibility 

• SQL/92    The || operator is the SQL/92 string concatenation operator.

• Sybase    The + operator is supported by Adaptive Server Enterprise.

  The || concatenation operator is not supported by Adaptive Server Enterprise.