![]() The COALESCE() function is a part of SQL ANSI-92 standard while NVL() function is Oracle specific. If you check for NULL in two expressions, the COALESCE() function is equivalent to the CASE expression.įor example, the following COALESCE() function: COALESCE(e1, e2)ĮND Code language: SQL (Structured Query Language) ( sql )ĮND Code language: SQL (Structured Query Language) ( sql ) Oracle COALESCE() vs. The COALESCE() function is more concise than a CASE expression that involves null evaluations. You can use the COALESCE() function instead of the longer CASE expression when it comes to test for null in multiple expressions. The following shows the result of the query: Oracle COALESCE() and CASE expression In case no phone numbers are available, we returned N/A literal string which stands for not available. In this example, we used the COALESCE() function to select home phone, work phone, or cell phone if each is available. INNER JOIN employees e USING (employee_id) The following query retrieves the employees and their emergency contacts with phone numbers: SELECTĮ.first_name || ' ' || e.last_name employee,Ĭ.first_name || ' ' || c.last_name contact,ĬOALESCE(home_phone, work_phone, cell_phone, 'N/A') phone Some contacts have only work phone while others may have a home phone and cell phone or don’t have any phone number at all. NULL ) Code language: SQL (Structured Query Language) ( sql ) INSERT INTO emergency_contacts ( employee_id, first_name, last_name, relationship, home_phone, work_phone, cell_phone ) The following statements insert some emergency contacts into the table: INSERT INTO emergency_contacts ( employee_id, first_name, last_name, relationship, home_phone, work_phone, cell_phone ) REFERENCES employees(employee_id) ON DELETE CASCADE To do it, you create a new table named emergency_contacts as follows: CREATE TABLE emergency_contacts (Ĭontact_id NUMBER GENERATED BY DEFAULT AS IDENTITY, Suppose you have to record emergency contacts of employees with various phone numbers: work phone, home phone, and cell phone. If it had done so, Oracle would have issued the division by zero error. It did not evaluate the second expression (1/0). In this example, the COALESCE() function only evaluated the first expression because the result of the first expression was two (1+1). It means that the function stops evaluating the remaining expressions once it finds the first one evaluates to a non-null value.Ĭonsider the following example: SELECT COALESCE( 1 + 1, 1/ 0) The COALESCE() function uses short-circuit evaluation. Oracle issued the following error: ORA-00932: inconsistent datatypes: expected NUMBER got CHARīecause the COALESCE() function tried to convert the character type of the third argument to a numeric type of the second argument that resulted in an error. However, the following example uses arguments of different types for the COALESCE() function: SELECT COALESCE( NULL, 1, 'A') Similarly, the following example returns a value with numeric type: SELECT COALESCE( NULL, 1, 2) result FROM SELECT COALESCE( NULL, 'A', 'B') result FROMĪ Code language: SQL (Structured Query Language) ( sql ) The following example returns a value with character type because all arguments are characters. In case the conversion fails, then Oracle issues an error. If the arguments have different data types, the COALESCE() function implicitly converts all arguments to the data type of the first non-null argument. If all arguments have the same data type, the COALESCE() function returns a value of that data type. ![]() The following example returns null because all arguments are null: SELECT COALESCE( NULL, NULL, NULL) - return NULL FROMĬode language: SQL (Structured Query Language) ( sql ) Return type The following example returns one because it is the first non-null argument: SELECT COALESCE( NULL, 1) - return 1 FROMĬode language: SQL (Structured Query Language) ( sql ) RESULT ![]() In case all expressions evaluate to null, the function returns null. In this syntax, the COALESCE() function returns the first non-null expression in the list. ![]() , en)Ĭode language: SQL (Structured Query Language) ( sql ) The following illustrates the syntax of the Oracle COALESCE() function: COALESCE(e1, e2. The Oracle COALESCE() function accepts a list of arguments and returns the first one that evaluates to a non-null value. Introduction to the Oracle COALESCE() function Summary: in this tutorial, you will learn how to use the Oracle COALESCE() function to return the first non-null arguments in a list. ![]()
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