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MySQLi Articles
Page 337 of 341
Is the primary key automatically indexed in MySQL?
Yes, primary key is automatically indexed in MySQL because primary key, index, etc gets stored into B-trees. All engines including InnoDB as well as MyISAM automatically supports the primary key to be indexed. The primary key is implicitly indexed in InnoDB, MyISAM, and other engines. Let us create a table with primary key − mysql> create table DemoIndex -> ( -> Id int not null, -> primary key(Id) -> ); Query OK, 0 rows affected (1.21 sec) In the above table, Id is implicitly indexed.
Read MoreRank function in MySQL?
The rank() function can be used to give a rank for every row within the partition of a result set. First, let us create a table − mysql> create table RankDemo mysql> ( mysql> id int mysql> ); Query OK, 0 rows affected (0.53 sec) Inserting records into table. mysql> insert into RankDemo values(1); Query OK, 1 row affected (0.19 sec) mysql> insert into RankDemo values(3); Query OK, 1 row affected (0.12 sec) mysql> insert into RankDemo values(3); Query OK, 1 row affected (0.11 ...
Read MoreCount the number of occurrences of a string in a VARCHAR field in MySQL?
To count the number of occurrences of a string in a VARCHAR, we can use the logic of subtraction with length. First, we will create a table with the help of create command. mysql> create table StringOccurrenceDemo -> ( -> Cases varchar(100), -> StringValue varchar(500) -> ); Query OK, 0 rows affected (0.56 sec) After executing the above table, we will insert records into the table. The query is as follows − mysql> insert into StringOccurrenceDemo values('First', 'This is MySQL Demo and MySQL is ...
Read MoreWhat is the operator <=> in MySQL?
Here are the usages of the operator in MySQL. Case 1 This operator is similar to = operator i.e. when the value is equal then the result will become true(1), otherwise false(0). In the first case both = and operators work same. Case 2 Whenever we compare any value with NULL then the operator gives the value 0 and when we compare with NULL NULL, then it returns 1. While in case of = operator, this does not happen. Whenever we compare any value with NULL, it returns NULL. If we compare NULL with NULL, then ...
Read MoreHow to set NOW() as default value for datetime datatype in MySQL?
We can set the now() function as a default value with the help of dynamic default. First, we will create a table with data type” datetime”. After that, we will set now() as the default value for column “MyTime” as shown below. Creating a table. mysql> create table DefaultDateTimeDemo -> ( -> MyTime datetime default CURRENT_TIMESTAMP -> ); Query OK, 0 rows affected (0.59 sec) After creating the above table, we won’t insert any value while using the insert command. This is done so that we can get the ...
Read MoreBest data type for storing currency values in a MySQL database?
For representation of money, we need to use Decimal (TotalDigitsinteger, DigitsAfterDecimalinteger) method. Let’s say, we need to display the value 345.66. For that, count how many digits are available. In value 345.66, there are 5 digits in total and 2 digits after decimal point, which is 66. We can represent the same with the help of Decimal() method from MySQL. Here is the exact representation. DECIMAL(5, 2) Let us first create a table and consider the same above representation for our example − mysql> create table MoneyRepresentation -> ( -> Money ...
Read MoreALTER TABLE to add a composite primary key in MySQL?
To add composite primary key, use the ALTER command. Let us first create a demo table The query to create a table. mysql> create table CompositePrimaryKey -> ( -> Id int, -> StudentName varchar(100), -> Age int -> ); Query OK, 0 rows affected (0.56 sec) Haven’t added composite primary key above till now. Let us now check with the help of desc command. mysql> desc CompositePrimaryKey; The following is the output. +-------------+--------------+------+-----+---------+-------+ | Field ...
Read MoreAlter a MySQL column to be AUTO_INCREMENT?
Let’s say we have a table and now there is a requirement to add AUTO_INCREMENT on column name. For that, use the MODIFY command. Here, we will create a demo table first. mysql> create table AddingAutoIncrement -> ( -> Id int, -> Name varchar(200), -> Primary key(Id) -> ); Query OK, 0 rows affected (0.47 sec) We have created a table above and now let us alter the table to add AUTO_INCREMENT on column name ‘Id’. The syntax is as follows − ...
Read MoreHow can I return 0 for NULL in MySQL?
We can return 0 for NULL in MySQL with the help of IFNULL() method. The syntax of IFNULL() is as follows. IFNULL(YOUREXPRESSION, 0); Let us see an example. First, we will create a table. mysql> create table NullDemoWithZero -> ( -> id varchar(200) -> ); Query OK, 0 rows affected (0.65 sec) After creating a table, let us insert some records in the table using the INSERT command. The query is as follows − mysql> insert into NullDemoWithZero values(); Query OK, 1 row affected (0.16 sec) ...
Read MoreHow to get a list of MySQL user accounts?
To get the list of MySQL user accounts, we can use “SELECT USER”. The following is the query to display the list. SELECT User FROM mysql.user; Here is the output. +------------------+ | User | +------------------+ | John | | Mac | | Manish | | mysql.infoschema | | mysql.session ...
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