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Articles by George John
Page 77 of 79
How to create a temporary MySQL table in a SELECT statement without a separate CREATE TABLE?
To create a temporary table in a SELECT statement we use TEMPORARY keyword. This temporary table will be visible for the current session and whenever a session is closed, it is automatically destroyed. Two sessions can use the same temporary table. Creating a table. mysql> create table MyTableDemo -> ( -> id int, -> Name varchar(100) -> ); Query OK, 0 rows affected (0.69 sec) Inserting some records. mysql> insert into MyTableDemo values(1, 'John'); Query OK, 1 row affected (0.18 sec) mysql> insert into MyTableDemo values(2, 'Carol'); Query OK, 1 row affected (0.13 ...
Read MoreHow do I check to see if a value is an integer in MySQL?
To check if the given value is a string or not ,we use the cast() function. If the value is not numeric then it returns 0, otherwise it will return the numeric value. In this way, we can check whether the value is an integer or not. Case 1 − Checking for a string with integers mysql> select cast('John123456' AS UNSIGNED); The following is the output. It shows that the value is not numeric, therefore 0 is returned. +--------------------------------+ | cast('John123456' AS UNSIGNED) | +--------------------------------+ | 0 | +--------------------------------+ 1 row in set, 1 warning (0.00 sec) ...
Read MoreHow to subtract 10 days from the current datetime in MySQL?
Firstly, let us get the current datetime with the help of the now() function. mysql> select now(); The following is the output. +---------------------+ | now() | +---------------------+ | 2018-11-01 19:55:56 | +---------------------+ 1 row in set (0.00 sec) Syntax to subtract 10 days with the help of DATE_SUB() select DATE_SUB(now(),interval integer_value day ); Applying the above syntax to subtract 10 days from the current datetime. mysql> select DATE_SUB(now(),interval 10 day); Here is the output. +---------------------------------+ | DATE_SUB(now(),interval 10 day) | +---------------------------------+ | 2018-10-22 19:56:07 | +---------------------------------+ 1 row in set (0.00 sec)
Read MoreGet the new record key ID from MySQL insert query?
We can get new record key with the help of LAST_INSERT_ID() function from MySQL. First, we will create a table and for inserting record, we will use LAST_INSERT_ID(). Let us create a table with the help of create command. The query is as follows − mysql> create table LastInsertRecordIdDemo -> ( -> id int auto_increment, -> value varchar(100), -> primary key(id) -> ); Query OK, 0 rows affected (0.52 sec) After creating a table, we will insert records and set it using LAST_INSERT_ID() ...
Read MoreUsage of backtick in SQL statements?
The backtick can be used in MySQL. To create a table, we can put table_name in backticks. Example of Backtick in MySQL. The CREATE command is used to create a table. Here, we have added the table name using the backtick symbol. mysql> create table `backtickSymbol` -> ( -> uniId int -> ); Query OK, 0 rows affected (1.65 sec) Records are inserted with the help of INSERT command. mysql> insert into `backtickSymbol` values(1); Query OK, 1 row affected (0.20 sec) mysql> insert into `backtickSymbol` values(2); Query ...
Read MoreMySQL status in terms of active or total connections?
The active or total connection can be known with the help of threads_connected variable. The variable tells about the number of currently open connections. The query is as follows − mysql> show status where `variable_name` = 'Threads_connected'; Here is the output. +-------------------+-------+ | Variable_name | Value | +-------------------+-------+ | Threads_connected | 1 | +-------------------+-------+ 1 row in set (0.06 sec) We can check the same with the help of show command. The query is as follows − mysql> show processlist; Here is the output. +----+-----------------+-----------------+----------+---------+--------+------------------------+------------------+ ...
Read MoreGenerating a unique random 10 character string using MySQL?
In order to generate a 10 character string, we can use inbuilt functions ‘rand()’ and ‘char()’. The following is the query to generate random 10 character string. mysql> SELECT concat( - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97), - > char(round(rand()*25)+97) - > )AS Random10CharacterString; ...
Read MoreWhich one is preferred between a large table or multiple small tables in MySQL?
It is very difficult to say whether to prefer one large table or multiple small tables. It depends − On the application we are using. On database normalization However, there are many key points, through which we can say that multiple small tables are good in that situation. Suppose many developers are going to develop multiple tables, then there is a need to split them into multiple small tables. A situation when you are giving authority to many developers. This authority is for different parts of data. In this case, a need arise to split into multiple small ...
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 MoreWhat does the KEY keyword mean in MySQL?
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 -> ( ...
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