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Database Articles
Page 438 of 546
How to get connected clients in MongoDB?
To get connected clients in MongoDB, use currentOp() with the set value to true and you need to iterate array result set with the help of field client. Let us first implement currentOp> db.currentOp(true)Following is the output. Here the client is 127.0.0.1 since we are using localhost. The output displays all the connected clients{ "inprog" : [ { "host" : "DESKTOP-QN2RB3H:27017", "desc" : "conn1", "connectionId" : 1, "client" : "127.0.0.1:61787", "appName" : "MongoDB Shell", ...
Read MoreWrite a MySQL query equivalent to “SHOW TABLES” in sorted order?
Use INFORMATION_SCHEMA.TABLES to display tables in sorted order. The below syntax will give sorted list of tables in ascending order:select TABLE_NAME from INFORMATION_SCHEMA.TABLES where TABLE_SCHEMA= 'yourDatabaseName' order by TABLE_NAME;Following is the query to implement the equivalent to SHOW TABLES:mysql> select TABLE_NAME from INFORMATION_SCHEMA.TABLES -> where TABLE_SCHEMA= 'sample' order by TABLE_NAME;This will produce the following output+------------------------------------+ | TABLE_NAME | +------------------------------------+ | a | | accumulateddemo ...
Read MoreWhat is the alias to Show Tables in MySQL Result?
You can use AS command for alias to show tables in MySQL result. Following is the syntax −SELECT TABLE_NAME AS anyAliasName FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = DATABASE();Let us implement the above syntax −mysql> SELECT TABLE_NAME AS MY_TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = DATABASE();This will produce the following output −+------------------------------------+ | MY_TABLE_NAME | +------------------------------------+ | a | | accumulateddemo | | add10minutedemo ...
Read MoreHow to count horizontal values on a MySQL database?
You can use aggregate function COUNT() from MySQL to count horizontal values on a database. Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstValue int, SecondValue int, ThirdValue int, FourthValue int ); Query OK, 0 rows affected (0.59 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(FirstValue, SecondValue, ThirdValue, FourthValue) values(-18, 45, 0, 155); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable(FirstValue, SecondValue, ThirdValue, FourthValue) values(0, 235, null, 15); Query OK, 1 row affected (0.20 sec)Following is the query to display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following ...
Read MoreCan I use InnoDB and MyISAM tables in a single database in MySQL?
Yes, you can use InnoDB and MyISAM tables in one database or combine both of them in a single database. This is the recommended way.Here is the demo of both MyISAM and InnoDB in a one database. The following is the database and both the table types InnoDB and MyISAM. The query to create a database is as follows −mysql> create database BothInnoDBandMyISAM; Query OK, 1 row affected (0.20 sec) mysql> use BothInnoDBandMyISAM; Database changedI have a database with name ‘BothInnoDBandMyISAM’.First the table has engine type InnoDB. The query to create a table with engine InnoDB is as follows −mysql> ...
Read MoreIs there a built-in function for week of the month in MySQL?
There is no standard function to get week of month in MySQL. You need to use the following syntax −SELECT WEEK(yourDateColumnName, 5) - WEEK(DATE_SUB(yourDateColumnName, INTERVAL DAYOFMONTH(yourDateColumnName) - 1 DAY), 5) + 1 AS anyAliasName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table FirstWeekOfMonth -> ( -> Id int NOT NULL AUTO_INCREMENT primary key, -> yourdate date -> ); Query OK, 0 rows affected (2.50 sec)Now you can insert some records in the table ...
Read MoreExtracting filenames from a path in MySQL?
To extract filenames from a path MySQL, you can use SUBSTRING_INDEX(). The syntax is as follows −SELECT SUBSTRING_INDEX(ypurColumnName, '\', -1) as anyAliasName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table ExtractFileNameDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> AllProgrammingFilePath varchar(100) -> ); Query OK, 0 rows affected (0.50 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> insert into ExtractFileNameDemo(AllProgrammingFilePath) ...
Read MoreChange max_heap_table_size value in MySQL?
The max_heap_table_size is a system variable that has both read/write property.Initially, max_heap_table_size has size 16 MB. First, check the value of max_heap_table_size, which is in bytes.The query is as follows −mysql> select @@max_heap_table_size;The following is the output −+-----------------------+ | @@max_heap_table_size | +-----------------------+ | 16777216 | +-----------------------+ 1 row in set (0.00 sec)Now let us how the value 16777216 byte = 16 MB −1 MB = 1024KB 1KB = 1024 Bytes 1MB = 1024*1024 bytes. To convert 16777216 byte to MB you need to divide 1024*1024. =16777216/(1024*1024) =16777216/1048576 ...
Read MoreInsert default into not null column if value is null in MySQL?
You can use IFNULL() property or simple IF() with IS NULL property. The syntax is as follows −INSERT INTO yourTableName(yourColumnName1, yourColumnName2) VALUES('yourValue’', IF(yourColumnName1 IS NULL, DEFAULT(yourColumnName2), 'yourMessage'));To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table Post -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> UserName varchar(10), -> UserPostMessage varchar(50) NOT NULL DEFAULT 'Hi Good Morning !!!' -> ); Query OK, 0 rows affected (0.67 sec)Now you can ...
Read MoreHow to correctly enclose subquery in MySQL?
You need to close the subquery in a parenthesis. The syntax is as follows −select if((select count(*) from yourTableName ), 'Yes', 'No') as anyAliasName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table SelectIfDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(10) -> ); Query OK, 0 rows affected (1.03 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into SelectIfDemo(Name) values('John'); Query OK, ...
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