Elasticsearch (sometimes dubbed ES) is a modern search and analytics engine which is based on Apache Lucene. Its built with Java, Elasticsearch is a NoSQL database. That means it stores data in an unstructured way and that you cannot use SQL to query it. This Elasticsearch tutorial could also be Read more
0. Data Preparation /*Table structure for table `user` */ DROP TABLE IF EXISTS `user`; CREATE TABLE `user` ( `id` int(11) NOT NULL auto_increment, `username` varchar(32) NOT NULL, `birthday` datetime default NULL, `sex` varchar(10) default NULL, `address` varchar(256) default NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; /*Data for the table Read more
Solution: Create a new tmp table Copy data to tmp table Delete original table Rename the tmp table’s name to original one’s # Step 1: CREATE TABLE tmp_table ( # your new column types ); # If you don't need to make any change CREATE TABLE tmp_table LIKE original_table; # Read more
1. If <select id="findActiveBlogWithTitleLike" resultType="Blog"> SELECT * FROM BLOG WHERE state = ‘ACTIVE’ <if test="title != null"> AND title like #{title} </if> </select> 2. Choose, When, Otherwise <select id="findActiveBlogLike" resultType="Blog"> SELECT * FROM BLOG WHERE state = ‘ACTIVE’ <choose> # choose only one case among many options <when test="title != Read more
Six Attributes collection: There are three formats: list, array, and map, according to the type of parameter passed. item: the parameter name of the set of objects in the tag. separator: the separator at the end of each sub-loop, usually “,”. open: start character, often “(“. close: end character, often Read more
SUBSTRING_INDEX(str, delim, count) str: the string to be split. delim: the delimiter. count: the position of the delimiter. A positive number means extract from left to right, a negative number means extract from right to left. For example: SELECT SUBSTRING_INDEX('100-200-300-400', '-', 1); — output: '100' SELECT SUBSTRING_INDEX('100-200-300-400', '-', 2); — Read more
When using mybatis as a persistence layer, insert, update, delete, sql statements do not return the primary key of the record being operated on by default, but rather the number of records being operated on. When we want to get the primary key automatically generated for the inserted data, we Read more
1. Index 1.1 Create Index Creating an index in ElasticSearch is like creating a database in a relational database.First we open postman to send the request. If you get this response, it has been successfully created. 1.2 View Index To view the shopping index, the command remains the same, except Read more
A JOIN clause is used to combine rows from two or more tables, based on a related column between them. There are four types of join in MySQL: INNER JOIN: Returns records that have matching values in both tables LEFT JOIN: Returns all records from the left table, and the matched records Read more
Atomicity: operations in a transaction either all succeed or all fail. Consistency: The database always transitions from one consistent state to another consistent state. The integrity of the database is not broken before the transaction starts and after the transaction ends. This means that the material written must fully comply Read more