How to add and subtract string numbers in sql

String numbers in SQL cannot be added or subtracted directly. This can be achieved using the following steps: Use CAST() to convert a string number to a numeric type; perform addition and subtraction operations; and optionally convert the result back to a string type.

Addition and subtraction of string numbers in SQL

In SQL, strings and numbers cannot be added directly Or subtract. Here's how to use SQL to convert string numbers to numbers and add and subtract them:

Step One: Type Conversion

UseCAST() Function converts string numbers into integer or floating point number types. For example:

<code class="sql">CAST('10' AS INTEGER) -- 将字符串 "10" 转换为整数 10
CAST('12.5' AS REAL) -- 将字符串 "12.5" 转换为浮点数 12.5</code>

Step 2: Addition and subtraction operations

Add and subtract the converted numbers. For example:

<code class="sql">SELECT CAST('10' AS INTEGER) + CAST('5' AS INTEGER); -- 输出：15
SELECT CAST('12.5' AS REAL) - CAST('5.5' AS REAL); -- 输出：7.0</code>

Step 3: Result type conversion (optional)

If necessary, the operation result can be converted back to the string type. For example:

<code class="sql">CAST(CAST('10' AS INTEGER) + CAST('5' AS INTEGER) AS TEXT); -- 输出：'15'
CAST(CAST('12.5' AS REAL) - CAST('5.5' AS REAL) AS VARCHAR(5)); -- 输出：'7.000'</code>

Note:

• The string must contain valid numbers, otherwise the conversion will fail.
• The converted result type depends on the format of the original string.
• Before performing addition and subtraction operations, ensure that string numbers have been correctly converted to numeric types.

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