The difference between varchar and varchar2 in oracle

VARCHAR and VARCHAR2 are both string data types in Oracle. The difference is: 1. VARCHAR allows NULL values, while VARCHAR2 does not; 2. VARCHAR ends with an implicit terminator "\0", while VARCHAR2 Ending with the explicit terminator "''"; 3. VARCHAR has a small storage overhead, and VARCHAR2 will additionally check the explicit terminator if it is large; 4. VARCHAR insertion and update efficiency is high, while VARCHAR2 query efficiency is slightly lower. Suggestion: Use VARCHAR if NULL values ​​are allowed or minimal storage overhead is required; if NULL values ​​are not allowed or

The difference between VARCHAR and VARCHAR2 in Oracle

VARCHAR and VARCHAR2 are both variable-length character data types used to store string data types in Oracle database. Although their names are similar, there are the following key differences between them:

1. NULL value handling:

• VARCHAR allows NULL values, that is, empty strings .
• VARCHAR2 does not allow NULL values ​​and can only store non-empty strings.

2. Default terminator:

• VARCHAR ends with the implicit terminator "\0".
• VARCHAR2 ends with an explicit terminator "''", which is an empty string.

3. Storage overhead:

• VARCHAR has less storage overhead because it only stores the actual length of the string.
• VARCHAR2 has greater storage overhead because it requires storing the explicit terminator of the string, even if the string is empty.

4. Performance:

• VARCHAR performs better during insert and update operations because only the actual data needs to be stored.
• VARCHAR2 has slightly lower performance in query operations because of the additional checks required for explicit terminators.

5. Character set support:

• VARCHAR and VARCHAR2 support all character sets supported by Oracle.

Usage recommendations:

• Use VARCHAR if NULL values ​​are allowed or minimal storage overhead is required.
• Use VARCHAR2 if NULL values ​​are not allowed or if you are dealing with large data volumes.

Example:

CREATE TABLE table_name (
  name VARCHAR(20) NULL,
  address VARCHAR2(50) NOT NULL
);

In this example:

• name The column is of type VARCHAR, NULL values ​​are allowed.
• address The column is of type VARCHAR2 and NULL values ​​are not allowed.

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