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mauricio
Asked: 2020-09-17 19:08:07 +0800 CST 2020-09-17 19:08:07 +0800 CST

How to insert data in a column that was created with alter table?

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I'm new to sql, the strange thing is that I use the alter table command to create a column called "height" when I insert his height look what happened.

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It is a lack of control that alter table only creates columns with null and when inserting data they run.

sql

2 Answers

  1. From what you show, I think you have a confusion regarding instructions.

    Insert data refers to inserting new rows to the table. So every time you insert something new rows will be created.

    When you create a column, all existing rows will have that column with the "value" NULLrepresenting an empty. This only if there is no default value for the column.

    What you want to do is update the already existing row to change the NULL value to the correct value. That is done with the instruction UPDATE.

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  2. Best Answer

    If you want to create a table, you don't need to use ALTER TABLE unless you want to modify a table that already exists.

    CREATE TABLE is used to create a new table, where the information is actually stored. ALTER TABLE is used to modify an existing table.

    Example of how to use ALTER TABLE:

    ALTER TABLE nombre_de_tabla ADD COLUMN nombre_de_columna definicion_de_columna;

    So with this you can see that you normally modify columns, and add one new field per column to the table, another real world example:

    ALTER TABLE empleados ADD age INT(11), name VARCHAR(40);

    And if what you want is that it does not appear: NULL, you must say NOT NULL at the end, to add a function to the column definition, like this:

    ALTER TABLE empleados ADD age INT(11), name VARCHAR(40) NOT NULL;

    UPDATE

    In your case, it should be something like this:

    ALTER TABLE information ALTER COLUMN height INT(40) NOT NULL;

    And to create a table, it's like this:

    CREATE TABLE Persons (name VARCHAR(40), age INT(11), height INT(11));

    I hope I have helped you, for more information you can go to: https://www.w3schools.com/sql/sql_create_table.asp

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