Found 4219 Articles for MySQLi

Key is synonymous to an index. If you want to create an index for a column, then use ‘Key’. As stated in the official docs: KEY is normally a synonym for INDEX. The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. This was implemented for compatibility with other database systems. The key can be used with Primary Key: Let us first create a table. Here is the query to set primary key for a column “id”. mysql> create table KeyDemo -> ( ... Read More

We can convert MySQL date and time to Unix Timestamp with the help of function UNIX_TIMESTAMP(). The following is the query. mysql> SELECT UNIX_TIMESTAMP(STR_TO_DATE('Oct 19 2018 10:00PM', '%M %d %Y %h:%i%p')); After running the above query we will not get the output in date format as shown in the below output. The output shown here is a Unix Timestamp. +------------------------------------------------------------------------+ | UNIX_TIMESTAMP(STR_TO_DATE('Oct 19 2018 10:00PM', '%M %d %Y %h:%i%p')) | +------------------------------------------------------------------------+ | ... Read More

We can remove the leading and trailing whitespaces from MySQL with the help of trim() function.The following is the syntax.mysql> SELECT TRIM(' AnyStringWithWhitespaces ');Let us now implement the above syntax in the below query.mysql> SELECT TRIM(' Leading And Trailing whitespaces Demo '); Here is the output that removes the whitespaces.+---------------------------------------+ | TRIM(' Leading And Trailing whitespaces Demo ') | +---------------------------------------+ | Leading And Trailing whitespaces Demo | +---------------------------------------+ 1 row in set (0.00 sec)Let us now see another way to remove the leading and trailing whitespaces.Firstly, let us create a new table.mysql> create table TrimDemo2 -> ( -> name varchar(200) ... Read More

We can use DISTINCT and COUNT together in a single MySQL query. Firstly, let us create a table. The CREATE command is used to create a table. mysql> create table DistCountDemo - > ( - > id int, - > name varchar(100), - > age int - > ); Query OK, 0 rows affected (0.48 sec) Records are inserted with the help of INSERT command. mysql> insert into DistCountDemo values(1, 'John', 23); Query OK, 1 row affected (0.11 sec) mysql> insert ... Read More

Unique in MySQL means we cannot add duplicate records. Let us now see how to create a unique constraint in the column at the time of creating a table.mysql> create table UniqueConstDemo - > ( - > name varchar(100) unique - > ); Query OK, 0 rows affected (0.72 sec)Now, we cannot have same value more than once for column ‘name’.Inserting some records with duplicate values to check the error.mysql> insert into UniqueConstDemo values('John'); Query OK, 1 row affected (0.19 sec) mysql> insert into UniqueConstDemo values('John');On running the above query, the following error is visible.mysql> insert into UniqueConstDemo values('John'); ... Read More

To add not null constraint to an existing column in MySQL, we will use the ALTER command. This is a type of validation to restrict the user from entering null values. Let us see an example. Firstly, we will create a table. The CREATE command is used to create a table. mysql> create table AddNotNUlldemo - > ( - > name varchar(100) - > ); Query OK, 0 rows affected (0.44 sec) To insert records. mysql> insert into AddNotNUlldemo values('John'); Query OK, 1 row affected (0.19 sec) ... Read More

To list running queries, we need to use the ‘show processlist’ command. The following is the query. mysql> SHOW processlist; The following is the output of the above query. +----+-----------------+-----------------+----------+---------+-------+------------------------+------------------+ | Id | User | Host | db | Command | Time | State | Info ... Read More

To insert current date/ time in MySQL, use the now() function. Let us now see an example.At first, we will create a table. The CREATE command is used to create a table.mysql > create table CurrentDateTime -> ( -> CurrentTime datetime -> ); Query OK, 0 rows affected (1.14 sec)Syntax to insert the current date/time with the help of insert command and now()mysql> insert into CurrentDateTime values(now()); Query OK, 1 row affected (0.11 sec)To check that the current date/ time is inserted in the table or not, use the select command.mysql> select *from CurrentDateTime; The following is the output that ... Read More

Let us see an example to get the count of each distinct value in a column. Firstly, we will create a table. The CREATE command is used to create a table. mysql> create table DistinctDemo1 - > ( - > id int, - > name varchar(100) - > ); Query OK, 0 rows affected (0.43 sec) Inserting records mysql> insert into DistinctDemo1 values(1, 'John'); Query OK, 1 row affected (0.34 sec) mysql> insert into DistinctDemo1 values(2, 'John'); Query OK, 1 row affected (0.20 sec) ... Read More

To return Sum as ‘0’ if no values are found, use IFNULL or COALESCE commands. The following is the syntax for IFNULL. SELECT IFNULL(SUM(NULL), 0) AS aliasName; Let us now implement the above syntax in the following query. mysql> SELECT IFNULL(SUM(NULL), 0) AS SUMOFTWO; The following is the output of the above query, which returns 0. +----------+ | SUMOFTWO | +----------+ | 0 | +----------+ 1 row in set (0.00 sec) Here is the syntax for COALESCE. mysql> SELECT COALESCE(SUM(NULL),0) as SUMOFTWO; The following is the output that returns 0 using the SUM() function. +----------+ | SUMOFTWO | +----------+ | 0 | +----------+ 1 row in set (0.00 sec)