learn sql in 21 days

The SQL date minus DATEDIFF () returns the number of days between two dates. The definition and usage of the DATEDIFF () function returns the number of days between two dates. The syntax DATEDIFF (date1, date2) date1 and date2 are valid date and time expressions. Note: Only the date part of the value is involved in calculation. DATEDIFF (expr1, expr2): returnsexp

this case, you need to normalize your table.18. Do not use the text data type whenever possibleDo not use text unless you use text to process a large amount of data. Because it is not easy to query and slow, it will waste a lot of space if it is not used well. Generally, varchar can better process your data.19. Try not to use temporary tablesTry not to use temporary tables unless you have. Generally, subqueries can replace temporary tables. Using a temporary table will bring about system overhe

Ten days to learn php (3 ). The seventh day of learning objective: to learn how to use a SESSION has many functions, most of which is to pass variables between pages on the site. At the beginning of the page, we want to start session_start (); enable the SESSION; and the seventh day of learning objective: to learn how

this.If (empty ($ _ Get ['page']){$ Page = 0;}Else{$ Page = $ _ Get ['page'];If ($ page If ($ page> = Ceil ($ num/10) $ page = Ceil ($ num/10)-1; // because page starts from 0, so-1} In this way, $ exec can write $ exec = "select * From tablename limit". ($ page * 10). ", 10 ";// One page is 10 records What we need to do at last is several connections: This is a general idea. You can think about how to optimize it? Today, let's talk about some important issues tomorrow.Day 9Objective: To

started for ten days, but proficient is by no means ten days. You need to study it on your own.Objective: To Learn How to Use PHP to upload files and send emailsEnctype = "multipart/form-data" must be added to the file upload form"And Let's take a look at the code below:$ F = $ HTTP_POST_FILES ['file'];$ Dest_dir = 'uploads'; // sets the upload directory.$ Dest

Ten days to learn php (2) third day objective: to learn how to build a database In ASP, if it is an ACCESS database, you can directly open ACCESS to edit the MDB file. if it is an SQL server, you can open the Enterprise Manager to edit the SQL SERVER database, but in PHP, t

Previously wrote 10 days to learn ASP, 10 days to learn ASP, and now think about writing a PHP bar, but also a comparison of all. PHP Debugging methods I do not say here, there are many articles are introduced, there are many different combinations. For the time being, I am using Apache Web server and my

Previously written 10 days to learn the ASP, 10 days to learn asp.net what, now think about writing a PHP bar, also calculate more complete. PHP Debugging methods I do not say here, outside a lot of articles are introduced, there are many different combinations. I'm here for the moment with the Apache Web server and my

Employeelistviewmodel = new Employeelistviewmodel ();4:5:employeebusinesslayer Empbal = new Employeebusinesslayer ();6:list7:8:list9:10:foreach (Employee emp in employees)11: {12:employeeviewmodel Empviewmodel = new Employeeviewmodel ();13:empviewmodel.employeename = emp. FirstName + "" + emp. LastName;14:empviewmodel.salary = emp. Salary.tostring ("C");15:if (EMP. Salary > 15000)16: {17:empviewmodel.salarycolor = "Yellow";18:}19:else20: {21:empviewm

Ten days to learn the sixth day of php, read ten days to learn the sixth day of php, objective: to learn to add and delete the modified data mysql_query ($ exec); this statement alone can execute all the operations, the difference is that the $ exec

Ten days to learn the third day of php objective: to learn how to build a database In ASP, if it is an ACCESS database, you can directly open ACCESS to edit the MDB file. if it is an SQL server, you can open the Enterprise Manager to edit the SQL SERVER database, but in PHP

Ten days to learn php (1 ). I used to learn ASP for ten days and ASP. NET for ten days. now I want to write another PHP, which is quite complete. I will not talk about the PHP debugging method here. many articles outside have introduced the process of learning ASP for ten

The third day of learning php in ten days. Objective: to learn how to build a database in ASP. for an ACCESS database, you can open ACCESS to edit the MDB file. for SQLSERVER, you can open the Enterprise Manager to edit S. objective: learn to build databases In ASP, if it is an ACCESS database, you can directly open ACCESS to edit the MDB file. if it is an

Previously wrote 10 days to learn ASP, 10 days to learn ASP, and now think about writing a PHP bar, but also a comparison of all. PHP Debugging methods I do not say here, there are many articles are introduced, there are many different combinations. For the time being, I am using Apache Web server and my

root 737603 Jan 5 21:40 setuptools-38.4.0.zip-rw-r--r--. 1 root root 418354 Jul Supervi Sor-3.3.3.tar.gz-rw-r--r--. 1 root root 802928 Jan 09:40 swoole-v2.0.10-stable.tar.gzdrwxr-xr-x. 2 root Root 4096 Feb 15:27 test-rw-r--r--. 1 root root 4 Feb 15:55 T.logPostscript1. Generate the Public key certificate thumbprintSsh-keygen-lf./ssh_host_rsa_key.pubResources"1" Man SCP"2" a Linux command per day: SCP commandHttps://www.cnblogs.com/p

I used to learn ASP for ten days and ASP. NET for ten days. now I want to write another PHP, which is quite complete. I won't talk about the debugging method of PHP here. many articles outside of the company have their advantages and different combinations. I am using I used to learn ASP for ten

of our common uses:1) VARCHAR, text type2) INT, integer type3) Float, floating-point type4) Date, type5) You may ask, where is the ID that is automatically added? just select the int type, and select Auto_increment in the extras below.After you have established the table, you can see the table you created on the left, and after clicking, you can:1) Press the structure on the right: View Modify table Structure2) Browse by right: View the data in the table3) Press the right

Ten days to learn php (1) I wrote ten days to learn ASP, and ten days to learn ASP. NET or something. now I want to write another PHP, which is quite complete. I will not talk about the PHP debugging method here. many articles hav

In the "Ten Days Learn ASP" tutorial, I rough introduced a bit ADO, in fact, can be said to be. It's just that the open method in the Connection object establishes a physical connection to the data source and disconnects it using the Close method; The changes made using the AddNew, Update, and Delete methods in the Recordset object refer to the AbsolutePage and RecordCount properties in the Recordset object

ADO in the "Ten Days Learn ASP" tutorial, I rough introduced a bit ADO, in fact, can be said to be. It's just that the open method in the Connection object establishes a physical connection to the data source and disconnects it using the Close method; The changes made using the AddNew, Update, and Delete methods in the Recordset object refer to the AbsolutePage and RecordCount properties in the Recordset ob