How to merge two column values ​​in oracle

How to merge two column values ​​using Oracle? Use the || operator to merge directly into a string. Use the CONCAT() function to merge multiple strings. Use the CASE statement to merge values ​​based on conditions.

How to merge two column values ​​using Oracle

Direct merge

The easiest way is to use the || operator to concatenate two columns into a string:

 <code>SELECT column1 || column2 FROM table_name;</code>

Using functions

You can also use the CONCAT() function, which concatenates multiple strings together:

 <code>SELECT CONCAT(column1, column2) FROM table_name;</code>

Conditions of use

If you need to merge values ​​based on conditions, you can use CASE statement:

 <code>SELECT CASE WHEN column1 IS NOT NULL THEN column1 WHEN column2 IS NOT NULL THEN column2 ELSE NULL -- 如果两列都为空，返回NULL END FROM table_name;</code>

Example

Suppose there is the following table:

 <code>CREATE TABLE my_table ( id INT PRIMARY KEY, first_name VARCHAR(255), last_name VARCHAR(255) ); INSERT INTO my_table (id, first_name, last_name) VALUES (1, 'John', 'Doe'), (2, 'Jane', 'Smith'), (3, NULL, 'Wilson');</code>

Direct merge

 <code>SELECT first_name || last_name AS full_name FROM my_table; ----------- | full_name | ----------- | John Doe | | Jane Smith | | Wilson | -- 返回NULL，因为first_name 为NULL -----------</code>

Using functions

 <code>SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM my_table; ----------- | full_name | ----------- | John Doe | | Jane Smith | | NULL Wilson | -- 返回NULL，因为first_name 为NULL -----------</code>

Conditions of use

 <code>SELECT CASE WHEN first_name IS NOT NULL THEN first_name WHEN last_name IS NOT NULL THEN last_name ELSE NULL END AS full_name FROM my_table; ----------- | full_name | ----------- | John Doe | | Jane Smith | | Wilson | -- 返回"Wilson"，因为last_name 不为空-----------</code>

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