SQL Coalesce | Coalesce function in sql - sql - sql tutorial - learn sql




  • Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.
 syntax opf coalesce function
  • The COALESCE function in SQL returns the first non-NULL expression among its arguments. The syntax for COALESCE is as follows:
COALESCE ("expression 1", "expressions 2", ...)
  • It is the same as the following CASE statement:
SELECT CASE ("column_name")
  WHEN "expression 1 is not NULL" THEN "expression 1"
  WHEN "expression 2 is not NULL" THEN "expression 2"
  ...
  [ELSE "NULL"]
  END
FROM "table_name";
  • For examples, say we have the following table,
  • Table Contact_Info
Name Business_Phone Cell_Phone Home_Phone
Neff 531-2531 622-7813 565-9901
Taura NULL 772-5588 312-4088
Arnold NULL NULL 594-7477
  • and we want to find out the best way to contact each person according to the following rules:
    • If a person has a business phone, use the business phone number.
    • If a person does not have a business phone and has a cell phone, use the cell phone number.
    • If a person does not have a business phone, does not have a cell phone, and has a home phone, use the home phone number.
  • We can use the COALESCE function to achieve our goal:
SELECT Name, COALESCE (Business_Phone, Cell_Phone, Home_Phone) Contact_Phone 
FROM Contact_Info;

Result:

Name Contact_Phone
Neff 531-2531
Taura 772-5588
Arnold 594-7477

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