Mysql query in php evaluates to true wrongly

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6 Answers

query
90%

You're not doing anything wrong: mysql_query statement returns true because it is executed correctly! This does not mean that any row gets updated in your database.,The returned result resource should be passed to mysql_fetch_array(), and other functions for dealing with result tables, to access the returned data.,somewhere I'm doing something wrong, my query results to true instead of false. In my table the id 246 does exist but the lev is zero in the table. What am I doing wrong, this query should result to false. It echo's success but it does not update the table.,For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.

It returns true because query was successfull and it affects 0 rows. If you want to check if something actually gets updated use

mysql_affected_rows
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88%

Note that expr1 is evaluated twice in MySQL if the arguments are equal.,Note that the period arguments P1 and P2 are not date values:,Note that the period argument P is not a date value:,The following table shows how the type and expr arguments are related:

(...)

Use parentheses to force the order of evaluation in an expression. For example:

mysql > SELECT 1 + 2 * 3; -
> 7
mysql > SELECT(1 + 2) * 3; -
> 9
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72%

Returns an array that corresponds to the fetched row and moves the internal data pointer ahead. ,Note: This function sets NULL fields to the PHP null value.,The result resource that is being evaluated. This result comes from a call to mysql_query().,mysql_data_seek() - Move internal result pointer

SELECT table1.field AS foo, table2.field AS bar FROM table1, table2
65%

There are several ways to see the names and values of system variables: , If enabled, the server stores all temporary tables on disk rather than in memory. This prevents most The table tbl_name is full errors for SELECT operations that require a large temporary table, but also slows down queries for which in-memory tables would suffice. , The variable can have two values: , Section 5.1.9.2, “Dynamic System Variables”, lists the variables that can be set at runtime.

To see the values that a server uses based on its compiled-in defaults and any option files that it reads, use this command:

mysqld--verbose--help
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75%

Why Stored Procedures?,Why Stored Procedures? ,Stored procedures are always available as 'source code' in the database itself. And it makes sense to link the data with the processes that operate on the data.,Variables in Stored Programs

Syntax:

CREATE[DEFINER = {
   user | CURRENT_USER
}]
PROCEDURE sp_name([proc_parameter[, ...]])[characteristic...] routine_body
proc_parameter: [IN | OUT | INOUT] param_name type
type:
   Any valid MySQL data type
characteristic:
   COMMENT 'string' |
   LANGUAGE SQL |
   [NOT] DETERMINISTIC |
   {
      CONTAINS SQL | NO SQL | READS SQL DATA |
      MODIFIES SQL DATA
   } |
   SQL SECURITY {
      DEFINER | INVOKER
   }
routine_body:
   Valid SQL routine statement
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40%

Although ignoring coding standards doesn’t directly lead to needing to debug PHP code, it is still probably one of the most important things to discuss here.,First let’s define a Regular class that includes test as a normal property:,Here’s an example of the kind of evasive and confusing bugs that this can lead to:,Here’s a small checklist to avoid such problems in your code:

Not sure how to use foreach loops in PHP? Using references in foreach loops can be useful if you want to operate on each element in the array that you are iterating over. For example:

$arr = array(1, 2, 3, 4);
foreach($arr as & $value) {
   $value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
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