Tag Archives: PHP

MySQL Cursor

A cursor can’t be used by itself in MySQL. It is an essential component in stored procedures. I would be inclined to treat a cursor as a “pointer” in C/C++, or an iterator in PHP’s foreach statement.

With cursors, we can traverse a dataset and manipulate each record to accomplish certain tasks. When such an operation on a record can also be done in the PHP layer, it saves data transfer amounts as we can just return the processed aggregation/statistical result back to the PHP layer (thus eliminating the select – foreach – manipulation process at the client side).

Since a cursor is implemented in a stored procedure, it has all the benefits (and limitations) of an SP (access control, pre-compiled, hard to debug, etc).

MySQL supports cursors inside stored programs. The syntax is as in embedded SQL. Cursors have these properties:

Asensitive: The server may or may not make a copy of its result table

Read only: Not updatable

Nonscrollable: Can be traversed only in one direction and cannot skip rows

Cursor declarations must appear before handler declarations and after variable and condition declarations.

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jQuery bind() vs .live() vs .delegate() vs .on()

All these 4 jQuery methods are used for attaching events to selectors or elements. But they all are different from each other.

.bind(): This is the easiest and quick method to bind events. But the issue with bind() is that it doesn’t work for elements added dynamically that matches the same selector. bind() only attach events to the current elements not future element. Above that it also has performance issues when dealing with a large selection.

.live(): This method overcomes the disadvantage of bind(). It works for dynamically added elements or future elements. Because of its poor performance on large pages, this method is deprecated as of jQuery 1.7 and you should stop using it. Chaining is not properly supported using this method.

.delegate(): The .delegate() method behaves in a similar fashion to the .live() method, but instead of attaching the selector/event information to the document, you can choose where it is anchored and it also supports chaining.

.on(): Since live was deprecated with 1.7, so new method was introduced named “.on()”. This method provides all the goodness of previous 3 methods and it brings uniformity for attaching event handlers.

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jQuery Difference Between .empty(), .remove() and .detach()

All these methods .empty(), .remove() and .detach() are used for removing elements from DOM but they all are different.

.empty(): This method removes all the child element of the matched element where remove() method removes set of matched elements from DOM.

.remove(): Use .remove() when you want to remove the element itself, as well as everything inside it. In addition to the elements themselves, all bound events and jQuery data associated with the elements are removed.

.detach(): This method is the same as .remove(), except that .detach() keeps all jQuery data associated with the removed elements. This method is useful when removed elements are to be reinserted into the DOM at a later time.

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