When used in a pl/sql block, which sql statement must return exactly one row?

Summary: in this tutorial, you will learn how to use the PL/SQL SELECT INTO statement to fetch data of a single row from a table into variables.

PL/SQL SELECT INTO statement is the simplest and fastest way to fetch a single row from a table into variables. The following illustrates the syntax of the PL/SQL SELECT INTO statement:

SELECT select_list INTO variable_list FROM table_name WHERE condition;

In this syntax, the number of columns in the variable_list must be the same as the number of variables (or the number of components of a record) in the select_list.  In addition, their corresponding data type must be compatible.

Besides the WHERE clause, you can use other clauses in the SELECT statement such as INNER JOIN, GROUP BY, HAVING, and UNION.

If the SELECT statement returns more than one row, Oracle will raise the TOO_MANY_ROWS exception. If the SELECT statement does not return any row, Oracle will raise the NO_DATA_FOUND exception.

PL/SQL SELECT INTO examples

Let’s use the customers and contacts tables in the sample database for demonstration.

A) PL/SQL  SELECT INTO – selecting one column example

The following example uses a SELECT INTO statement to get the name of a customer based on the customer id, which is the primary key of the customers table.

DECLARE l_customer_name customers.name%TYPE; BEGIN SELECT name INTO l_customer_name FROM customers WHERE customer_id = 100; dbms_output.put_line( v_customer_name ); END;

In this example:

• First, declare a variable l_customer_namewhose data type anchors to the name columns of the customers table. This variable will hold the customer name.
• Second, use the SELECT INTO statement to select value from the name column and assign it to the l_customer_name variable.
• Third, show the customer name using the dbms_output.put_line procedure.

Because the customers table has only one row with customer ID 100, the code block displayed the customer name.

If there were no such row, the code block would fail with an unhandled NO_DATA_FOUND exception.

B) PL/SQL SELECT INTO – selecting a complete row example

The following example fetches the entire row from the customers table for a specific customer ID:

DECLARE r_customer customers%ROWTYPE; BEGIN SELECT * INTO r_customer FROM customers WHERE customer_id = 100; dbms_output.put_line( r_customer.name || ', website: ' || r_customer.website ); END;

Here is the output:

In this example:

• First, declare a record based on the row of the customers table. This record will hold the entire row of the customers table.
• Second, select the customer whose id is 100 into the r_customer record.
• Third, show the customer’s name and website.

C) PL/SQL SELECT INTO – selecting data into multiple variables example

The following example fetches the names of customer and contact from the customers and contacts tables for a specific customer id.

DECLARE l_customer_name customers.name%TYPE; l_contact_first_name contacts.first_name%TYPE; l_contact_last_name contacts.last_name%TYPE; BEGIN SELECT name, first_name, last_name INTO l_customer_name, l_contact_first_name, l_contact_last_name FROM customers INNER JOIN contacts USING( customer_id ) WHERE customer_id = 100; dbms_output.put_line( l_customer_name || ', Contact Person: ' || l_contact_first_name || ' ' || l_contact_last_name ); END;

Oracle issued the following output:

Verizon, Contact Person: Elisha Lloyd

In this example:

• First, declare three variables l_customer_name, l_contact_first_name, l_contact_last_name to hold the customer and contact’s name.
• Second, use the SELECT INTO statement to fetch customer and contact names of the customer id 100 from the customers and contacts tables into the corresponding variables
• l_customer_name, l_contact_first_name, l_contact_last_name.
• Third,  display the customer and contact names.

PL/SQL SELECT INTO common errors

If the number of columns and expression in the SELECT clause is greater than the number of variables in the INTO clause, Oracle issues this error:

ORA-00947: not enough values The INTO list contains fewer variables than the SELECT list.

Oracle issues the following error if the number of columns and expression in the SELECT clause is less than the number of variables in the INTO clause:

ORA-00913: too many values The INTO list contains more variables than the SELECT list.

If the number of variables and element in the select list are the same, but their corresponding datatypes are not compatible so that Oracle cannot implicitly convert from one type to the other. It will issue the following error:

ORA-06502: PL/SQL: numeric or value error

Now, you should know how to use the PL/SQL SELECT INTO statement to fetch a single row from a table into variables.

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