The logical structure of Damon database is very similar to Oracle, but it is very different from MySQL and sqlserver. Damon database has no concept of database. From top to bottom, it is in the order of instance user table. See the figure for details; Pay attention to the one to many relationship. When establishing each object, it is necessary to clarify the relationship between objects, what to establish first, what to establish later, who controls what, and what to manage. Here we briefly introduce the following important concepts: database, instance, user, tablespace, schema, table, role, and data file. 1. The physical medium for database data storage. Broadly speaking, any physical medium that stores data can be called a database, such as a word document. But in fact, we say that databases are generally

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Foreword Recently, I met in my work that a field in a table is extensible data content, and the information is generated by comma separation. Now we need to show the content related to the query of this field data in other tables. The first idea is to cut the data, using comma as the cutting character. The following is the general implementation method for your reference and guidance. 1. The regexp_substr function is used to split strings by regularization. The function usage is: (It must be supported by the version of Oracle 10g+) REGEXP_SUBSTR The function format is as follows: function REGEXP_SUBSTR (String, pattern, position, occurrence, modifier) __src