how to get information about data types in postgresql with code examples

Introduction

PostgreSQL is an open-source, object-relational database management system (ORDBMS) that is widely used for managing large amounts of data. It provides a rich set of data types that allow developers to store and manage different types of data in a structured and efficient manner. In this article, we will explore various data types in PostgreSQL and how you can retrieve information about them.

Data Types in PostgreSQL

PostgreSQL supports a wide range of data types, including:

Numeric Types:
- SMALLINT
- INTEGER
- BIGINT
- DECIMAL
- NUMERIC
- REAL
- DOUBLE PRECISION
Character Types:
- CHAR
- VARCHAR
- TEXT
Binary Data Types:
- BYTEA
Date and Time Types:
- DATE
- TIME
- TIMESTAMP
- INTERVAL
Boolean Type:
- BOOLEAN
Bit Strings:
- BIT
- VARBIT
Geometric Types:
- POINT
- LINE
- LSEG
- BOX
- PATH
- POLYGON
- CIRCLE
Network Address Types:
- INET
- CIDR
- MACADDR
Bit Strings:
- BIT
- VARBIT
UUID Type:
- UUID
JSON Types:
- JSON
- JSONB
Enumerated Types:
- ENUM

Retrieving Information about Data Types in PostgreSQL

There are several ways to retrieve information about data types in PostgreSQL:

Using the Information Schema

The information schema in PostgreSQL provides a set of views that contain metadata about the database, including information about data types. The following query retrieves the information about all data types in the database:

SELECT typname, typtype, typcategory, typbasetype
FROM pg_catalog.pg_type
ORDER BY typname;

The typname column provides the name of the data type, typtype shows whether it is a base type, domain type, or composite type, typcategory provides information about the type category, and typbasetype provides the OID of the base type for a domain type or composite type.

Using the pg_type System Catalog

The pg_type system catalog in PostgreSQL provides information about the data types in the database. The following query retrieves information about all data types in the database:

SELECT oid, typname, typtype
FROM pg_type
ORDER BY typname;

The oid column provides the object identifier (OID) of the data type, typname provides the name of the data type, and typtype shows whether it is a base type, domain type, or composite type.

Using the pg_type_info Function

The pg_type_info function in PostgreSQL provides information about a specific data type. The following query retrieves information about the integer data type:

SELECT pg_type_info('integer');

Using PostgreSQL Data Types in Tables

Once you have a good understanding of the different data types available in PostgreSQL, you can start using them in your tables. When creating a table, you can specify the data type for each column. For example, the following SQL statement creates a table named `employee` with three columns, `id`, `name`, and `hire_date`:

CREATE TABLE employee (
id serial PRIMARY KEY,
name varchar(50) NOT NULL,
hire_date date NOT NULL
);

In this example, the `id` column is of type `serial`, which is an auto-incrementing integer, the `name` column is of type `varchar` with a maximum length of 50 characters, and the `hire_date` column is of type `date`.

Data Type Conversion in PostgreSQL

In some cases, you may need to convert data from one data type to another. PostgreSQL provides several functions for converting data types, including:

- `CAST`: This function converts a value from one data type to another data type. For example, the following statement converts a string to an integer:

SELECT CAST('123' AS integer);

- `CONVERT`: This function converts a value from one data type to another data type. The function syntax is similar to the `CAST` function.

- Type-specific conversion functions: PostgreSQL also provides type-specific conversion functions for certain data types, such as `date` and `timestamp`. For example, the following statement converts a string to a date:

SELECT to_date('2022-01-01', 'YYYY-MM-DD');

Conclusion

In this article, we have explored the different data types in PostgreSQL and how to retrieve information about them. We have also discussed how to use data types in tables and how to convert data from one data type to another. With this knowledge, you can effectively manage and manipulate data in your PostgreSQL database.
## Popular questions 
1. How do you retrieve information about all data types in PostgreSQL?
Answer: You can retrieve information about all data types in PostgreSQL by querying the `pg_type` system catalog table. The following SQL statement will return information about all data types:

SELECT * FROM pg_type;

2. How do you retrieve information about a specific data type in PostgreSQL?
Answer: You can retrieve information about a specific data type in PostgreSQL by querying the `pg_type` system catalog table and filtering by the type name. For example, to retrieve information about the `varchar` data type, you can run the following SQL statement:

SELECT * FROM pg_type WHERE typname = 'varchar';

3. How do you retrieve information about the maximum length of a `varchar` data type in PostgreSQL?
Answer: You can retrieve information about the maximum length of a `varchar` data type in PostgreSQL by querying the `pg_type` system catalog table and filtering by the type name. The `typlen` column in the `pg_type` table contains information about the maximum length of the data type. For example, the following SQL statement will return the maximum length of a `varchar` data type:

SELECT typlen FROM pg_type WHERE typname = 'varchar';

4. How do you retrieve information about the storage size of a data type in PostgreSQL?
Answer: You can retrieve information about the storage size of a data type in PostgreSQL by querying the `pg_type` system catalog table and filtering by the type name. The `typlen` column in the `pg_type` table contains information about the storage size of the data type. For example, the following SQL statement will return the storage size of an `integer` data type:

SELECT typlen FROM pg_type WHERE typname = 'integer';

5. How do you retrieve information about the input and output functions of a data type in PostgreSQL?
Answer: You can retrieve information about the input and output functions of a data type in PostgreSQL by querying the `pg_type` system catalog table and filtering by the type name. The `typinput` and `typoutput` columns in the `pg_type` table contain information about the input and output functions of the data type. For example, the following SQL statement will return the input and output functions of a `varchar` data type:

SELECT typinput, typoutput FROM pg_type WHERE typname = 'varchar';

### Tag 
PostgreSQL Data Types.

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