UPDATE MySQL queries. MySQL Reference Guide Mysql update number of rows updated

If we need to change or update data in MySQL, we can use the SQL UPDATE command to work. ,

grammar

Below is the UPDATE command to change MySQL data Sheet Data General SQL syntax:

UPDATE table_name SET field1=new-value1, field2=new-value2

• You can update one or more fields at the same time.
• You can specify any condition in the WHERE clause.
• You can also update data in a separate table.

When you need to update the data specified in the rows of a table, INEKE is very useful.

Command line to update data

Below we will update the w3big_tbl specified in the data table using the SQL UPDATE command:

examples

The following example will update the data table as w3big_title w3big_id field value 3:

# mysql -u root -p password; Enter password:******* mysql> use w3big; Database changed mysql> UPDATE w3big_tbl -> SET w3big_title="Learning JAVA" -> WHERE w3big_id=3; Query OK, 1 row affected (0.04 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> !}

Use PHP script to update data

PHP function to use mysql_query() to execute SQL statements, you can use the UPDATE SQL statement or INEKE does not apply.

This function in MySQL> command line the effect of executing SQL statements is the same.

examples

The following example will update the w3big_id data in the w3big_title 3 field.

UPDATE command— makes changes to an existing record or multiple records in a table SQL. Modifies existing values ​​in a table or the view's main table.

UPDATE Command Command Syntax

UPDATE Command Syntax

UPDATE command. Basic keywords and parameters of the UPDATE command

• schema - a permission identifier, usually the same as some username
• table view - table name SQL, in which the data is changed; if a view is defined, the data is modified in the main table SQL submissions
• subquery_1 - subquery, which the server treats in the same way as a view
• Witholumn - table column SQL or submissions SQL, whose value changes; if the table column is from a sentence SET is omitted, the column value remains unchanged
• expr - ; this expression may contain main variables and optional indicator variables
• subquery_2 - new value assigned to the corresponding column
• subquery_3 - new value assigned to the corresponding column

WHERE- defines the range of rows to be modified by those for which a certain condition is TRUE; if this phrase is omitted, all rows in the table or view are modified.
When an approval is issued, any UPDATE trigger, defined on the table.
Subqueries. If the offer SET contains subquery, it returns exactly one row for each row modified. Each value in the subquery result is assigned to the corresponding list columns in parentheses. If the subquery does not return any rows, the column is assigned NULL. Subqueries can select data from the modified table. Offer SET can combine expressions and subqueries.

UPDATE Command Example 1
Changing the rating for all buyers to a value equal to 200:

Customers SET rating = 200;

UPDATE Command Example 2
Replacing a column value across all rows of a table is generally rarely used. Therefore in the team, as in the team DELETE, you can use a predicate. To perform the specified replacement of the rating column values, for all customers who are served by the seller Giovanni (snum = 1003), you should enter:

Customers SET rating = 200 WHERE snum = 1001;

SQL UPDATE Command Example 3
In a sentence SET You can specify any number of values ​​for the columns, separated by commas:

Emp SET job = 'MANAGER', sal = sal + 1000, deptno = 20 WHERE ename = 'JONES';

UPDATE Command Example 4
In a sentence SET you can specify a NULL value without using any special syntax (such as IS NULL). Thus, if you want to set all customer ratings from London (city = 'London') to NULL, you would enter:

Customers SET rating = NULL WHERE city = 'London';

UPDATE Command Example 5
Explains the use of the following command syntax:

• Both sentence forms SET together in one statement.
• Subquery.
• A WHERE clause that limits the range of rows that can be modified.

Emp a SET deptno =
(SELECT deptno FROM dept WHERE loc = 'BOSTON'), (sal, comm) = ( SELECT 1.1*AVG(sal), 1.5*AVG(comm) FROM emp b WHERE a.deptno = b.deptno) WHERE deptno IN ( SELECT deptno FROM dept WHERE loc = 'DALLAS' OR loc = 'DETROIT');

The above statement does the following:

• Modifies only those employees who work in Dallas or Detroit
• Sets the value of the deptno column for employees from Boston
• Sets the salary of each employee at 1.1 times the average salary of the entire department
• Sets each employee's commission at 1.5 times the average commission for the entire department

UPDATE tbl_name SET col_name1=expr1 [, col_name2=expr2, ...]

The UPDATE statement updates columns with their new values ​​in the rows of an existing table. The SET statement specifies which columns should be modified and what values ​​should be set in them. The WHERE clause, if present, specifies which rows are updated. Otherwise, all rows are updated. If an ORDER BY expression is specified, the rows will be updated in the order specified in it.

If indicated keyword LOW_PRIORITY , then execution of this UPDATE command is delayed until other clients have finished reading this table.

If the IGNORE keyword is specified, the update command will not abort even if the update encounters a duplicate key error. Rows that cause conflicts will not be updated.

If a column is accessed from the specified expression by the tbl_name argument, then the UPDATE command uses the current value for that column. For example, the following command sets the age column to a value one greater than its current value:

Mysql> UPDATE persondata SET age=age+1;

The UPDATE command assigns values ​​from left to right. For example, the following command duplicates the age column, then increments it:

Mysql> UPDATE persondata SET age=age*2, age=age+1;

If a column is set to its current value, then MySQL notices this and does not update it.

The UPDATE command returns the number of rows actually changed. In MySQL version 3.22 and later, the C API function mysql_info() returns the number of rows that were found and updated and the number of warnings that occurred when UPDATE was executed.

In MySQL version 3.23, you can use LIMIT # to ensure that only the specified number of rows have been modified.

This MySQL tutorial explains how to use the MySQL UPDATE statement with syntax and examples.

Syntax

In its simplest form, the syntax for the UPDATE statement when updating one table in MySQL is:

UPDATE table SET column1 = expression1, column2 = expression2, ... ;

However, the full syntax for the MySQL UPDATE statement when updating one table is:

UPDATE [ LOW_PRIORITY ] [ IGNORE ] table SET column1 = expression1, column2 = expression2, ... ] ;

The syntax for the UPDATE statement when updating one table with data from another table in MySQL is:

UPDATE table1 SET column1 = (SELECT expression1 FROM table2 WHERE conditions) ;

The syntax for the MySQL UPDATE statement when updating multiple tables is:

UPDATE table1, table2, ... SET column1 = expression1, column2 = expression2, ... WHERE table1.column = table2.column AND conditions;

Parameters or Arguments

LOW_PRIORITY Optional. If LOW_PRIORITY is provided, the update will be delayed until there are no processes reading from the table. LOW_PRIORITY may be used with MyISAM, MEMORY and MERGE tables that use table-level locking. IGNORE Optional. If IGNORE is provided, all errors encountered during the update are ignored. If an update on a row would result in a violation of a primary key or unique index, the update on that row is not performed. column1, column2 The columns that you wish to update. expression1, expression2 The new values ​​to assign to the column1, column2. So column1 expression1, column2 would be assigned the value of expression2, and so on. WHERE conditions Optional. The conditions that must be met for the update to execute. ORDER BY expression Optional. It may be used in combination with LIMIT to sort the records appropriately when limiting the number of records to be updated. LIMIT number_rows Optional. If LIMIT is provided, it controls the maximum number of records to update in the table. At most, the number of records specified by number_rows will be update in the table.

Example - Update single column

Let's look at a very simple MySQL UPDATE query example.

UPDATE customers SET last_name = "Anderson" WHERE customer_id = 5000;

This MySQL UPDATE example would update the last_name to "Anderson" in the customers table where the customer_id is 5000.

Example - Update multiple columns

Let's look at a MySQL UPDATE example where you might want to update more than one column with a single UPDATE statement.

UPDATE customers SET state = "California", customer_rep = 32 WHERE customer_id > 100;

When you wish to update multiple columns, you can do this by separating the column/value pairs with commas.

state to "California" and the customer_rep to 32 where the customer_id is greater than 100.

Example - Update table with data from another table

Let's look at an UPDATE example that shows how to update a table with data from another table in MySQL.

UPDATE customers
SET city = (SELECT city
FROM suppliers
WHERE suppliers.supplier_name = customers.customer_name)
WHERE customer_id > 2000;

This UPDATE example would update only the customers table for all records where the customer_id is greater than 2000. When the supplier_name from the suppliers table matches the customer_name from the customers table, the city from the suppliers table would be copied to the city field in the customers table.

Example - Update multiple Tables

Let's look at a MySQL UPDATE example where you might want to perform an update that involves more than one table in a single UPDATE statement.

UPDATE customers, suppliers SET customers.city = suppliers.city WHERE customers.customer_id = suppliers.supplier_id;

This MySQL UPDATE statement example would update the city field in the customers table to the city from the suppliers table where the customer_id matches the supplier_id.

What is the DELETE Keyword?

The SQL DELETE command is used to delete rows that are no longer required from the database tables. It deletes the whole row from the table. Delete command comes in handy to delete temporary or obsolete data from your database.The DELETE command can delete more than one row from a table in a single query. This proves to be advantages when removing large numbers of rows from a database table.

Once a row has been deleted, it cannot be recovered. It is therefore strongly recommended to make database backups before deleting any data from the database. This can allow you to restore the database and view the data later on should it be required.

Delete command syntax

The basic syntax of the delete command is as shown below.

• DELETE FROM `table_name` tells MySQL server to remove rows from the table ..
• is optional and is used to put a filter that restricts the number of rows affected by the DELETE query.

If the WHERE clause is not used in the DELETE query, then all the rows in a given table will be deleted. Before we go into more details discussion the DELETE command, let's insert some sample data into the movies table to work with.

INSERT INTO `movies` (`title`, `director`, `year_released`, `category_id`) VALUES ("The Great Dictator", "Chalie Chaplie", 1920, 7); INSERT INTO `movies` (`title`, `director`, `category_id`) VALUES ("sample movie", "Anonymous", 8); INSERT INTO movies (`title`, `director`, `year_released`, `category_id`) VALUES ("movie 3", "John Brown", 1920, 8);

Executing the above script adds three (3) movies into the movies table. Before we go any further into our lesson, let"s get all the movies in our table. The script shown below does that.

SELECT * FROM `movies`;

movie_id	itle	director	year_released	category_id
1	Pirates of the Caribbean 4	Rob Marshall	2011	1
2	Forgetting Sarah Marshal	Nicholas Stoller	2008	2
3	X-Men	NULL	2008	NULL
4	Code Name Black	Edgar Jimz	2010	NULL
5	Daddy's Little Girls	NULL	2007	8
6	Angels and Demons	NULL	2007	6
7	Davinci Code	NULL	2007	6
9	Honey mooners	John Schultz	2005	8
16	67% Guilty	NULL	2012	NULL
18	The Great Dictator	Chalie Chaplie	1920	7
19	sample movie	Anonymous	NULL	8
20	movie 3	John Brown	1920	8

Let"s suppose that the Myflix video library no longer wishes to be renting out "The Great Dictator" to its members and they want it removed from the database. Its movie id is 18, we can use the script shown below to delete its row from the movies table.

Executing the above script in MySQL WorkBench against the Myflix deletes the movie with id 18 from the database table.

Let's see the current status of movies table.

SELECT * FROM `movies`;

movie_id	title	director	year_released	category_id
1	Pirates of the Caribbean 4	Rob Marshall	2011	1
2	Forgetting Sarah Marshal	Nicholas Stoller	2008	2
3	X-Men	NULL	2008	NULL
4	Code Name Black	Edgar Jimz	2010	NULL
5	Daddy's Little Girls	NULL	2007	8
6	Angels and Demons	NULL	2007	6
7	Davinci Code	NULL	2007	6
9	Honey mooners	John Schultz	2005	8
16	67% Guilty	NULL	2012	NULL
19	sample movie	Anonymous	NULL	8
20	movie 3	John Brown	1920	8

• the movie with id 18 has not been return in the query result set.
• you cannot delete a single column for a table. You can delete an entire row.

Let's say we have a list of movies we want to delete . We can use the WHERE clause along with IN.

Executing the above script deletes movies with IDs 20 and 21 from our movies table.

WHAT IS THE UPDATE COMMAND?

The Update command is used to modify rows in a table. The update command can be used to update a single field or multiple fields at the same time. It can also be used to update a table with values ​​from another table .

Update command syntax

The basic syntax of the SQL Update command is as shown below.

• UPDATE `table_name` is the command that tells MySQL to update the data in a table .
• SET `column_name` = `new_value" are the names and values ​​of the fields to be affected by the update query. Note, when setting the update values, strings data types must be in single quotes. Numeric values ​​do not need to be in quotation marks. Date data type must be in single quotes and in the format "YYYY-MM-DD".
• is optional and can be used to put a filter that restricts the number of rows affected by the UPDATE query.

Let's now look at a practical example that updates data in the members table. Let's suppose that our member's membership numbers 1 and 2 have the following updates to be made to their data records.

Membership number	Updates required
1	Changed contact number from 999 to 0759 253 532
2	Change the name to Janet Smith Jones and physical address should be updated to Melrose 123

We will start with making updates for membership number 1 before we make any updates to our data, let"s retrieve the record for membership number 1. The script shown below helps us to do that.

Executing the above script gives us the following results.

membership_number	full_names	gender	date_of_birth	physical_address	postal_address	contct_number	email
1	Janet Jones	Female	21-07-1980	First Street Plot No. 4	Private Bag	999

Let's now update the contact number using the script shown below.

Executing the above script updates the contact number from 999 to 0759 253 532 for membership number 1. Let's now look at the record for membership number 1 after executing the update script.

Executing the above script gives us the following results.

membership_number	full_names	gender	date_of_birth	physical_address	postal_address	contct_number	email
1	Janet Jones	Female	21-07-1980	First Street Plot No. 4	Private Bag	0759 253 542	This email address is being protected from spambots. You need JavaScript enabled to view it.

Let's now look at the updates required for membership number 2.

membership_number	full_names	gender	date_of_birth	physical_address	postal_address	contct_number	email
2	Smith Jones	Female	23-06-1980	Park Street	NULL	NULL	This email address is being protected from spambots. You need JavaScript enabled to view it.

The following script helps us to do that.

Executing the above script in updates the full names for membership number 2 to Janet Smith Jones and the physical address to Melrose 123.

membership_number	full_names	gender	date_of_birth	physical_address	postal_address	contct_number	email
2	Janet Smith Jones	Female	23-06-1980	Melrose 123	NULL	NULL	This email address is being protected from spambots. You need JavaScript enabled to view it.

Summary

• The delete command is used to remove data that is no longer required from a table.
• The "WHERE clause" is used to limit the number of rows affected by the DELETE query.
• Once data has been deleted, it cannot be recovered, it is therefore strongly recommend making backups before deleting data.
• The update command is used to modify existing data.
• The "WHERE clause" is used to limit the number of rows affected by the UPDATE query.