mainframe database types

result of the "leftmost prefix". The simple understanding is only from the left to the beginning of the combination. Not as long as the combined index is used for queries that contain these three columns, the following SQL uses this combined MySQL database index:SELECT * FROM MyTable whree username= "admin" and city= "Zhengzhou" select * FROM MyTable whree username= "admin" and the next few will not be used:SELECT * FROM MyTable whree age=20 and city

In the forum, there will be different types of posts, such as: General paste, essence, top posts;These posts in the Forum are sorted according to the different types, not just the type of posts, but also the dynamics of the postings.Here's a simple sort of post, and we're just looking at the latest dynamic time of the post and the sort of post type.The latest dynamic time is determined: if you just created

stream of characters to output the sound.Long string types are not commonly used. Personal privacy, voice, image, computer was lost, to repair the computer is also OK. //------------------------------------------------------------------------------------------------------------- -----Three. Date and Time typeDate only recorded on 2015-01-14Time is only recorded 11:36:25Year Only records years 2015Datatime record date and record time 2015-01

: Integer data from 0 to 255.Bit:1 or 0 of integer data.(4) decimal and numericBoth of these data types are equivalent. have two parameters: P (Precision) and S (decimal digits). p Specifies the maximum number of decimal digits that can be stored to the left and right of the decimal point, and P must be a value from 1 to 38. s specifies the maximum number of decimal digits that can be stored to the right of the decimal point, s must be a value from 0

Main Oracle Data Types Overview: The data types supported by various databases are similar to those in standard SQL languages. Type: varchar2: You can set the maximum length of a field when declaring it. After using it, you do not have to consider the existence of spaces. If the length of the inserted string is lower than the upper limit, the system automatically reduces it to the true length of the string.

Key-Value Store databaseTemporary: as memcached. The temporary key-value database stores the data in memory, which in two cases results in the loss of data, the first is the power outage, but the data content exceeds the memory size. The benefits of this treatment are very fast.Permanent type: such as Tokyo Tyrant, flare and RomaThe two are both types: Redis. Redis first data in memory, and then meet certai

, name2) VALUES (:name, :name)"); // ... query.bindValue(":name", name); 1 2 3 Only the first: name placeholder can be bound, and cannot be bound to the second one. Next we still use the same query object to execute a SELECT statement. If there is a query result, Qsqlquery::next () returns true until the end of the result is reached and false to indicate that the traversal is complete. We use this to iterate through the results of the query using the while loop. Use the Q

basic lock types in the database: Exclusive Locks (X lock) and Share Locks (S lock ). When an exclusive lock is applied to a data object, other transactions cannot read or modify it. Data Objects with a shared lock can be read by other transactions, but cannot be modified. The database uses these two basic lock types

Data type:Integer type: bigint, int, smallint, mediumint, tinyintDecimal type: decimal, numericFloat type: Real, float, doubleBit type: bitCharacter type: char, varchar, LongVarChar, longtextUnicode character type: nchar, nvarcharTextual: Text, TinytextBinary type: binary, varbinaryDateTime type: Date, time, DateTime, timestamp, yearThe Datetime range is: 1753.1.1--9999.12.31smalldatetime range is: 1900.1.1--2079.6.6Create a database: Right-click the

Whether in a small free database space or a large e-commerce website, it is necessary to reasonably design the table structure and make full use of the space. This requires us to fully understand the Common Data Types of database systems. Next I will share some of my experiences with you. I. digit type The number types