# UPDATE

# Basic Update

# Updating one row

UPDATE customers SET email='luke_smith@email.com' WHERE id=1

This query updates the content of email in the customers table to the string luke_smith@email.com where the value of id is equal to 1. The old and new contents of the database table are illustrated below on the left and right respectively:

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# Updating all rows

UPDATE customers SET lastname='smith'

This query update the content of lastname for every entry in the customers table. The old and new contents of the database table are illustrated below on the left and right respectively:

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Notice: It is necessary to use conditional clauses (WHERE) in UPDATE query. If you do not use any conditional clause then all records of that table's attribute will be updated. In above example new value (Smith) of lastname in customers table set to all rows.

# Update with Join Pattern

Consider a production table called questions_mysql and a table iwtQuestions (imported worktable) representing the last batch of imported CSV data from a LOAD DATA INFILE. The worktable is truncated before the import, the data is imported, and that process is not shown here.

Update our production data using a join to our imported worktable data.

UPDATE questions_mysql q -- our real table for production 
join iwtQuestions i -- imported worktable 
ON i.qId = q.qId
SET q.closeVotes = i.closeVotes,
q.votes = i.votes, 
q.answers = i.answers, 
q.views = i.views;

Aliases q and i are used to abbreviate the table references. This eases development and readability.

qId, the Primary Key, represents the Stackoverflow question id. Four columns are updated for matching rows from the join.

# UPDATE with ORDER BY and LIMIT

If the ORDER BY clause is specified in your update SQL statement, the rows are updated in the order that is specified.

If LIMIT clause is specified in your SQL statement, that places a limit on the number of rows that can be updated. There is no limit, if LIMIT clause not specified.

ORDER BY and LIMIT cannot be used for multi table update.

Syntax for the MySQL UPDATE with ORDER BY and LIMIT is,

UPDATE [ LOW_PRIORITY ] [ IGNORE ]
tableName
SET column1 = expression1,
    column2 = expression2,
    ...
[WHERE conditions]
[ORDER BY expression [ ASC | DESC ]]
[LIMIT row_count];

---> Example
UPDATE employees SET isConfirmed=1 ORDER BY joiningDate LIMIT 10

In the above example, 10 rows will be updated according to the order of employees joiningDate.

# Multiple Table UPDATE

In multiple table UPDATE, it updates rows in each specified tables that satisfy the conditions. Each matching row is updated once, even if it matches the conditions multiple times.

In multiple table UPDATE, ORDER BY and LIMIT cannot be used.

Syntax for multi table UPDATE is,

UPDATE [LOW_PRIORITY] [IGNORE] 
table1, table2, ...
    SET column1 = expression1,
        column2 = expression2,
        ...
    [WHERE conditions]

For example consider two tables, products and salesOrders. In case, we decrease the quantity of a particular product from the sales order which is placed already. Then we also need to increase that quantity in our stock column of products table. This can be done in single SQL update statement like below.

UPDATE products, salesOrders
  SET salesOrders.Quantity = salesOrders.Quantity - 5, 
      products.availableStock = products.availableStock + 5
WHERE products.productId = salesOrders.productId
  AND salesOrders.orderId = 100 AND salesOrders.productId = 20;

In the above example, quantity '5' will be reduced from the salesOrders table and the same will be increased in products table according to the WHERE conditions.

# Bulk UPDATE

When updating multiple rows with different values it is much quicker to use a bulk update.

UPDATE people 
SET name = 
  (CASE id WHEN 1 THEN 'Karl'
           WHEN 2 THEN 'Tom'
           WHEN 3 THEN 'Mary'
   END)
WHERE id IN (1,2,3);

By bulk updating only one query can be sent to the server instead of one query for each row to update. The cases should contain all possible parameters looked up in the WHERE clause.

# Syntax

  • UPDATE [ LOW_PRIORITY ] [ IGNORE ] tableName SET column1 = expression1, column2 = expression2, ... [WHERE conditions]; //Simple single table update

  • UPDATE [ LOW_PRIORITY ] [ IGNORE ] tableName SET column1 = expression1, column2 = expression2, ... [WHERE conditions] [ORDER BY expression [ ASC | DESC ]] [LIMIT row_count]; //Update with order by and limit

  • UPDATE [LOW_PRIORITY] [IGNORE] table1, table2, ... SET column1 = expression1, column2 = expression2, ... [WHERE conditions]; //Multiple Table update