Concatenation Operator
Syntax
concatenation_operator ::= "||"
concatenate_expression ::= add_expression ("||" add_expression)*Semantics
The concatenation operator returns the character string made by joining the operands in the given order. The operands can be of any* type. For more details, see the concat Function section.
                  
Note:
According to the operator precedence, the || operator is immediately after +, - (as binary operators).Example 6-85 Concatenation Operator
This example joins id, firstname, and lastname into a single string and provides the output. Notice that id, which is an integer type, also gets concatenated with the string values.
SELECT id || firstname || lastname AS name FROM users +-------------+
 |    name     |
 +-------------+
 | 10JohnSmith |
 | 30PeterPaul |
 | 20MaryAnn   |
 +-------------+