MySQL使用默认值添加列，使用QUOTES语法

I am doing well with mySql, but when it comes to some quirks I am struck.

This is something I used for years successfully

$sql = "ALTER TABLE " . $Tablu . " ADD " . $Colu . " varchar(" . intVal($Siza) .")";

What I want now is just add a DEFAULT value for the new column I am adding. Please provide a syntax WITH THE EXISTING STRUCTURE of the query. That is with THE QUOTES

I am trying this

$sql = "ALTER TABLE " . $Tablu . " ADD " . $Colu . " varchar(" . intVal($Siza) .") DEFAULT ('" . $defa . "')";

But it is NOT working

I CANNOT understand the without-quotes-mysql game at all.

Thanks in advance

you query is ok .. you just need to remove those brackets () around $defa.. like this-

$sql = "ALTER TABLE " . $Tablu . " ADD " . $Colu . " varchar(" . intVal($Siza) .") DEFAULT '" . $defa . "'";

This might be the correct way to do it.

$sql = "ALTER TABLE " . $Tablu . " ADD " . $Colu . " varchar(" . intVal($Siza) ." DEFAULT 'default_value')";

You can set the default value in the quotes itself using

SET DEFAULT 'value' OR SET DEFAULT NULL

Your query will be like

$sql = "ALTER TABLE " . $Tablu . " ADD " . $Colu . " varchar(" . intVal($Siza) .")" . " SET DEFAULT " . $defa;