![]() ![]() PostgreSQL grants database access via roles that are used to specify privileges. The trailing “%” in “last_name LIKE ‘S%’” says find all strings that start with an “S”. The way you defined the “LIKE” operator was such that the query checked every “last_name” value to find values that started with an “S”. Run the following query on “employees_1” with a “LIKE” operator: SELECT * FROM employees_1 WHERE last_name LIKE 'S%' Īn output similar to the following appears: In that case, you can use the partial match PostgreSQL operator “LIKE.” Let’s try to pull out complete row information where “last_name” in the “employees_1” table starts with an “S”. But let’s say if you are trying to find a record where you don’t remember the exact row value. For example, to extract all rows from “employees_1” where someone’s last name is “Doe,” we can run the following command: SELECT * FROM employees WHERE last_name = 'Doe' You can run a range of operations where we can extract relevant information from these databases. This creates a new table named “employees_new” with “last_name” as “Doe.” To check our new table, we can run the following command: SELECT * FROM employees_new SELECT * FROM employees WHERE last_name = 'Doe' Run the syntax above on the “employees” table and find rows with “last_name” as “Doe” To do this, type the following command: CREATE TABLE employees_new AS ![]() To illustrate this syntax, create a new table “employees_new” when “last_name” is equal to “Doe”. To create a new table where you selectively wish to keep only rows with certain information, use the following syntax to create a new table: CREATE TABLE AS To merge both tables by updating either of these tables, merge “employees_1” by updating data in the “employees” table: INSERT INTO employees SELECT * FROM employees_1 where not exists(SELECT * FROM employees where employee_id=employees_1.employee_id and first_name=employees_1.first_name and last_name=employees_1.last_name) Īn output similar to the following appears, when you try: SELECT * FROM employees employee_id | first_name | last_name To do so, run the following command: SELECT * FROM employees union SELECT * FROM employees_1 Use the union command to merge both tables. Update the table “employees” with a new row and view contents of “employees”: SELECT * FROM employees employee_id | first_name | last_name Merge the “employees” table with another table “employees_1.”Ĭreate a new table “employees_1” and view the contents of “employees_1”: SELECT * FROM employees_1 employee_id | first_name | last_name It’s also possible to merge two database tables. View the contents of the “employees” table: SELECT * FROM employees Īn output similar to the following appears: employee_id | first_name | last_name Insert a record into the table: INSERT INTO employees VALUES (1, 'John', 'Doe') Run the commands in this section from the PostgreSQL shell, opened in Step 2 of the Create a Database section.Ĭreate a table called “employees” in the test database: CREATE TABLE employees (employee_id int, first_name varchar, last_name varchar) When creating the tables, you may specify as many parameters (columns) as you need and name them appropriately. This section contains examples that create a test database with an employee’s first and last name, assigning each a unique key. You may find more information on a specific command by adding it after \h.Įxit the PostgreSQL shell by entering the \q command. To see a list of available commands, use the \h command. This is the PostgreSQL client shell, in which you can issue SQL commands. The output is similar to the following: psql (9.5.25) Run the commands in this section as the postgres Linux user.Ĭreate a sample database called mytestdb: createdb mytestdbĬonnect to the test database: psql mytestdb. See the Secure Local PostgreSQL Access section for information about changing this setting. Peer authentication will be used by default for local connections. The password set in this step will be used to connect to the database via the network. The Linux user is used to access the database, and the PostgreSQL user is used to perform administrative tasks on the databases. This user is distinct from the postgres Linux user. ![]()
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