Database Articles - Page 399 of 546

To calculate the average of values in a row in MySQL, use the following syntaxSELECT (yourTableName.yourColumnName1+yourTableName.yourColumnName2+yourTableName.yourColumnName3+, ..........N)/numberOfColumns AS anyAliasName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table calculateAverageDemo    -> (    -> x int,    -> y int,    -> z int    -> ); Query OK, 0 rows affected (1.41 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into calculateAverageDemo values(10, 20, 30); Query OK, 1 row affected (0.78 sec) mysql> insert into calculateAverageDemo values(40, 50, 70); Query ... Read More

The contact() method is used to concatenate. However, lower() is used to change the case to lowercase. For our example, let us create a table.The query to create a table is as followsmysql> create table concatAndLowerDemo    -> (    -> FirstValue varchar(10),    -> SecondValue varchar(10),    -> ThirdValue varchar(10),    -> FourthValue varchar(10)    -> ); Query OK, 0 rows affected (0.55 sec)Now you can insert some records in the table using insert command.The query is as followsmysql> insert into concatAndLowerDemo values('John', '12345', 'Java', 'MySQL'); Query OK, 1 row affected (0.21 sec) mysql> insert into concatAndLowerDemo values('Hi', '12345', ... Read More

You can use COALESCE() along with aggregate function MAX() for this.The syntax is as followsSELECT COALESCE(MAX(`yourColumnName`), 0) FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table avoidNullDemo    -> (    -> `rank` int    -> ); Query OK, 0 rows affected (0.53 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into avoidNullDemo values(10); Query OK, 1 row affected (0.20 sec) mysql> insert into avoidNullDemo values(NULL); Query OK, 1 row affected (0.18 sec) mysql> insert into avoidNullDemo values(20); Query OK, 1 ... Read More

The return type of count is long. The Java statement is as followsrs.next(); long result= rs.getLong("anyAliasName");First, create a table with some records in our sample database test3. The query to create a table is as followsmysql> create table CountDemo    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> Name varchar(20)    -> ); Query OK, 0 rows affected (0.60 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into CountDemo(Name) values('John'); Query OK, 1 row affected (0.21 sec) mysql> insert into CountDemo(Name) values('Carol'); Query OK, 1 row affected (0.16 sec) ... Read More

To fix this error, you need to specify the -p option for password.The syntax is as followsmysql -uyourUserName -pLet us implement it.First, we need to open CMD using Windows+R shortcut keys. The snapshot is as followsType CMD and press OK button. You will get a command prompt.The snapshot is as followsNow reach the MySQL bin directory.The snapshot is as followsNow use the syntax discussed in the beginning.The command is as follows

The AND has the highest priority than the OR operator in MySQL select query.Let us check how MySQL gives the highest priority to AND operator.The query is as followsmysql> select 0 AND 0 OR 1 as Result;The following is the output+--------+ | Result | +--------+ | 1     | +--------+ 1 row in set (0.00 sec)If you are considering the OR operator has the highest priority then MySQL will wrap up the above query like this.The query is as followsselect 0 AND (0 OR 1) as ResultFirst, solve the 0 OR 1, this will give result 1. After that ... Read More

You can use the distinct command for this. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.distinctCountValuesDemo.insertOne({"StudentFirstName":"John", "StudentFavouriteSubject":["C", "C++", "Java", "MySQL", "C", "C++"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a39f193b406bd3df60e07") } > db.distinctCountValuesDemo.insertOne({"StudentFirstName":"Larry", "StudentFavouriteSubject":["MongoDB", "SQL Server"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a3a1193b406bd3df60e08") }Display all documents from a collection with the help of find() method. The query is as follows −> db.distinctCountValuesDemo.find().pretty();The following is the output −{    "_id" : ObjectId("5c8a39f193b406bd3df60e07"),    "StudentFirstName" : "John",    "StudentFavouriteSubject" : [ ... Read More

You can use the aggregate framework to find duplicate records in MongoDB. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a330293b406bd3df60e01") } > db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a330493b406bd3df60e02") } > db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a330c93b406bd3df60e03") } > db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"Sam"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a331093b406bd3df60e04") } > db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"Carol"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a331593b406bd3df60e05") } > db.findDuplicateRecordsDemo.insertOne({"StudentFirstName":"Mike"}); {   ... Read More

For this, use the $not operator in MongoDB. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.notLikeOperatorDemo.insertOne({"StudentName":"John Doe"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a29c393b406bd3df60dfc") } > db.notLikeOperatorDemo.insertOne({"StudentName":"John Smith"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a29cc93b406bd3df60dfd") } > db.notLikeOperatorDemo.insertOne({"StudentName":"John Taylor"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a29df93b406bd3df60dfe") } > db.notLikeOperatorDemo.insertOne({"StudentName":"Carol Taylor"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a2a1693b406bd3df60dff") } > db.notLikeOperatorDemo.insertOne({"StudentName":"David Miller"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8a2a2693b406bd3df60e00") }Display all documents from ... Read More

Do not use $ symbol or period (.) because these characters are not allowed for MongoDB field names. The field shouldn’t start with $.Here is an example of the allowed characters −> db.charactersAllowedDemo.insertOne({"Employee Name" : "John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c7fefbc8d10a061296a3c6d") }Display all documents from a collection with the help of find() method. The query is as follows −> db.charactersAllowedDemo.find().pretty();The following is the output −{    "_id" : ObjectId("5c7fefbc8d10a061296a3c6d"),    "Employee Name" : "John" }