SQL: EXISTS Condition. This SQL tutorial explains how to use the SQL EXISTS condition with syntax and examples.
Click the Try It button next to an example to test it for yourself in our SQL Editor. Description. The SQL EXISTS condition is used in combination with a subquery and is considered to be met, if the subquery returns at least one row. It can be used in a SELECT, INSERT, UPDATE, or DELETE statement. Syntax. The syntax for the EXISTS condition in SQL is: WHERE EXISTS ( subquery ); Parameters or Argumentssubquery.
This SQL tutorial explains how to use the SQL EXISTS condition with syntax and examples. The SQL EXISTS condition is used in combination with a subquery and is.
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The subquery is a SELECT statement. If the subquery returns at least one record in its result set, the EXISTS clause will evaluate to true and the EXISTS condition will be met. If the subquery does not return any records, the EXISTS clause will evaluate to false and the EXISTS condition will not be met. Note. SQL statements that use the EXISTS condition are very inefficient since the sub- query is rerun for EVERY row in the outer query's table. There are more efficient ways to write most queries, that do not use the EXISTS condition. DDL/DML for Examples. If you want to follow along with this tutorial, get the DDL to create the tables and the DML to populate the data.
IF and else IF. 1> 2> CREATE FUNCTION fnFirstName (@FullName VarChar(100) 3>, @FirstOrLast VarChar(5)) 4> RETURNS VarChar(100) 5> AS 6> BEGIN. I have a table: Message (MessageID int, Subject nvarchar(100), Body nvarchar(max)) After a message is being updated on UI, I call a stored proc to update that table.
Then try the examples in your own database! Get DDL/DMLExample - Using EXISTS Condition with the SELECT Statement. Let's start by looking at an example that shows how to use the EXISTS condition with a SELECT statement. In this example, we have a customers table with the following data: customer_idlast_namefirst_namefavorite_website. Jackson. Joetechonthenet.
- · As T-SQL programmers, we always hear that the SQL language is optimized for set-based solutions rather than procedural solutions, but we seldom see.
- The basic components of a Merge statement are explained, as well as common pitfalls like handling NULL values.
- · UPDATE(column) can be used anywhere inside the body of a Transact-SQL trigger. Examples. The following example.
Smith. Janedigminecraft. Ferguson. Samanthabigactivities. Reynolds. Allencheckyourmath. Anderson. Paige. NULL9. Johnson. Derektechonthenet. And a table called orders with the following data: order_idcustomer_idorder_date.
Now let's find all of the records from the customers table where there is at least one record in the orders table with the same customer_id. Enter the following SELECT statement: Try It. SELECT *. WHERE customers. There will be 4 records selected.
These are the results that you should see: customer_idlast_namefirst_namefavorite_website. Jackson. Joetechonthenet. Smith. Janedigminecraft. Reynolds. Allencheckyourmath. Anderson. Paige. NULLIn this example, there are 4 records in the customers where the customer_id value appears in the orders table.
Example - Using EXISTS Condition with the UPDATE Statement. Let's look at an example that uses the EXISTS condition in an UPDATE statement. In this example, we have a table called products with the following data: product_idproduct_namecategory_id. Pear. 50. 2Banana. Orange. 50. 4Apple.
Bread. 75. 6Sliced Ham. Kleenex. NULLAnd a table called summary_data with the following data: product_idcurrent_category. Now let's update the summary_data table with values from the products table.
Enter the following SQL statement: UPDATE summary_data. SET current_category = (SELECT category_id. FROM products. WHERE products. WHERE EXISTS (SELECT category_id. FROM products. WHERE products.
There will be 5 records update. Select the data from the summary_data table again: SELECT * FROM summary_data; These are the results that you should see: product_idcurrent_category. This example would update the current_category field in the summary_data table with the category_id from the products table where the product_id values match. The first 5 records in the summary_data table have been updated.
TIP: If we hadn't included the EXISTS condition, the UPDATE query would have updated the current_category field to NULL in the 6th row of the summary_data table (because the products table does not have a record where product_id=8). Example - Using EXISTS Condition with the DELETE Statement. Let's look at an example that uses the EXISTS condition in a DELETE statement.
In this example, we have a table called customers with the following data: customer_idlast_namefirst_namefavorite_website. Jackson. Joetechonthenet.
Smith. Janedigminecraft. Ferguson. Samanthabigactivities. Reynolds. Allencheckyourmath.
Anderson. Paige. NULL9. Johnson. Derektechonthenet. And a table called orders with the following data: order_idcustomer_idorder_date.
NULL2. 01. 6/0. 5/0. Enter the following DELETE statement: DELETE FROM orders. FROM customers. WHERE customers.
AND customers. last_name = 'Jackson'); There will be 1 record deleted. Select the data from the orders table again: SELECT * FROM orders; These are the results that you should see: order_idcustomer_idorder_date. NULL2. 01. 6/0. 5/0. This example would delete all records from the orders table where there is a record in the customers table with the last_name of 'Jackson' and a matching customer_id value in both tables.
In this example, the record for order_id=4 was deleted. If you want to determine the number of rows that will be deleted, you can run the following SELECT statement before performing the delete. SELECT COUNT(*) FROM orders.
FROM customers. WHERE customers. AND customers. last_name = 'Jackson'); This will return number of records that will be deleted when you execute the DELETE statement. Example - Using NOT with the EXISTS Condition. Finally, the NOT condition can be combined with the EXISTS condition to create a NOT EXISTS condition. Let's look at an example that shows how to use the NOT EXISTS condition in SQL. In this example, we have a table called customers with the following data: customer_idlast_namefirst_namefavorite_website. Jackson. Joetechonthenet.
Anderson. Paige. NULL9. Johnson. Derektechonthenet. And a table called orders with the following data: order_idcustomer_idorder_date. NULL2. 01. 6/0. 5/0.
Enter the following SQL statement: Try It. SELECT *. WHERE NOT EXISTS. WHERE customers. customer_id = orders. There will be 2 records selected. These are the results that you should see: customer_idlast_namefirst_namefavorite_website.
Ferguson. Samanthabigactivities. Johnson. Derektechonthenet.
This example would return all records from the customers table where there are no records in the orders table for the given customer_id.
How do you update a Date. Time field in T- SQL? Using a Date. Time parameter is the best way.
However, if you still want to pass a Date. Time as a string, then the CAST should not be necessary provided that a language agnostic format is used. Given a table created like : create table t. End. Date DATETIME). End. Date) values (1, GETDATE()). The following should always work : update t.
End. Date = '2. 01. YYYYMMDD is language agnostic. The following will work : SET LANGUAGE us_english. End. Date = '2. 01. However, this won't : SET LANGUAGE british. End. Date = '2. 01. This is because 'YYYY- MM- DD' is not a language agnostic format (from SQL server's point of view) .
The ISO 'YYYY- MM- DDThh: mm: ss' format is also language agnostic, and useful when you need to pass a non- zero time. More info : http: //www. SQLServer/info_datetime.