ENVIRONMENT VARIABLES IN PostgreSQL: These are useful to avoid hard-coding database connection information into simple client applications, for example. To start a PostgreSQL server, you can run the following command:
|
1 |
[postgres@postgres1 ~]$ /usr/local/pgsql/bin/pg_ctl –D /u01/data start |
However, you can also use an environmental variable to create a shortcut for this… Read More
CLUSTER AND MULTICLUSTERS IN POSTGRESQL: In PostgreSQL Before you can start a PostgreSQL server, you need to create a cluster. A cluster refers to a collection of databases managed by a single instance of the PostgreSQL server. When you install PostgreSQL, It doesn’t automatically create… Read More
MongoDB Query Operators Part-3 Evaluation Query Operators MongoDB Evaluation operators are used to evaluate the structure of overall data or the individual fields in the document. They are of six types of Evaluations operators 1. mod ($mod) 2. text ($text) 3. where ($where) 4. jsonSchema… Read More
MongoDB Query Operators Part-2 Element Query Operator This operator is used to find the documents based on the datatypes and the fields in a document. There are two element query operators. 1. exists ($exists) 2. type ($type) 1. exist ($exist): This operator is used to… Read More
Clauses and filters: Like clause:
|
1 2 3 4 5 6 7 |
college=# select * from report where temp_hi:: text like '4%'; place | temp_lo | temp_hi | date | humidity | precp ----------------------------------------------------------- VZG | 32 | 43 | 2023-05-10 | 21 | HYD | 32 | 43 | 2020-07-19 | 24 | BZA | 32 | 43 | 2023-05-09 | 23 | (3 rows) |
LIMIT Clause: The LIMIT clause is used to restrict the number of rows returned in the result set. It is useful when you want to retrieve only a certain number of rows.
|
1 2 3 4 5 6 7 8 |
college=# select * from report LIMIT 4; place | temp_lo | temp_hi | date | humidity | precp ----------------------------------------------------------- VZG | 32 | 43 | 2023-05-10 | 21 | HYD | 32 | 43 | 2020-07-19 | 24 | BZA | 32 | 43 | 2023-05-09 | 23 | Delhi | 23 | 34 | 2023-05-15 | 24 | (4 rows) |
OFFSET Clause: It is used in conjunction… Read More
JOIN OPERATION IN PostgreSQL: In PostgreSQL, the JOIN clause is used to combine rows from two or more tables based on a related column or condition. It specifies how the tables should be joined and on which columns the join should be performed. There are… Read More
MongoDB Query Operators There are different types of Operators available in MongoDB which are used to filter the data. 1 – Comparison operators 2 – Logical operators 3 – Element operators 4 – Evaluation operators 5 – Geospatial operators 6 – Array operators 7 –… Read More
In PostgreSQL, “ALTER” and “UPDATE” are two different SQL commands used to modify data in a database. “ALTER” is used to modify the structure of the database, while “UPDATE” is used to modify the data stored within the database. Update: The UPDATE command plays a… Read More
MongoDB CRUD Operations 1 – To create a new database called sample data. Atlas atlas-dsrabt-shard-0 [primary] myFirstDatabase> use sample data. 2 – To create a new collection called students. Atlas atlas-dsrabt-shard-0 [primary] sampledata> db.createCollection(“students”). 3 – To insert one document in to the collection called… Read More
CREATING A NEW TABLE You can create a new table by specifying the table name, along with all column names and their types. Syntax for table creation: CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, columnN datatype, PRIMARY KEY (one or more columns) ); An example for creating table on weather… Read More
