Previously, we introduced the classes related to metadata management in CryptDB and the storage format of these classes in MySQL. This article describes when these metadata were created, when and how they were written to the database, when they were read, and where they were used.
Initialization and Metadata Readin ...
Added by reidme on Thu, 16 May 2019 22:45:15 +0300
Why query for table joins?
Query employee information with department name SALES
How do I join queries to tables?
Two ways: Sql 1992 and sql1999
sql1992sql classificationCartesian product (table multiplier)2. Use'='for the join condition of the equivalence join table3. Join conditions for non-equal join tables use'>, >=, <, <=,! ...
Added by chauffeur on Thu, 16 May 2019 08:02:13 +0300
Oracle database client has an sqlplus component that allows us to perform some database operations on the command line. In order to improve the efficiency of dump file writing, we try to use sqlplus command to generate dump file.
sqlplus can specify running scripts, such as:
sqlplus admin/pwd@//127.0.0.1:1526/orcl@./tmp_sql/N ...
Added by jonasr on Thu, 16 May 2019 06:48:26 +0300
In order to facilitate learning and testing, all the examples are built under Oracle's own user Scott.
Note: The red order by in the title indicates that order by must be taken when using this method.1. rank ()/ dense_rank () over (partition by... Order by...)
Now customers have such a need to query the information of t ...
Added by Dragonfly on Thu, 16 May 2019 05:30:30 +0300
Added by wiggly81 on Thu, 16 May 2019 00:18:55 +0300
Brief: The eighth day was recorded today (only eight days were written).Sometimes I see more, sometimes I see less, and then I save a few days to write together.Today, I wrote this plugin for an afternoon yesterday. I went back after work. I ended it today and added a process diagram to help understand the following principles.I have been readi ...
Added by tmaiden on Wed, 15 May 2019 23:32:20 +0300
General database role privilege handling in SQL Server Recently, we have been doing database privilege cleanup with colleagues, mainly by deleting some accounts, removing the larger privileges of some accounts, etc. For example, some have db_owner privileges, we remove the database role db_owner of the accounts and grant the minimum required ...
Added by Karpathos on Wed, 15 May 2019 18:59:55 +0300
1.java.lang.NullPointerException (Runtime Exception) is a runtime exception that the compiler cannot predict, such as when you define a Reference variable String a, but you did not instantiate the variable with the new keyword.
There are two solutions to this null pointer exception, because you call this a's method againif(null!=a) this variabl ...
Added by ypirc on Wed, 15 May 2019 13:47:55 +0300
PostgreSQL, brin index, gin index, merge delay, gin_pending_list_limit, query performance degradation
GIN index is an inverted index of PostgreSQL database with multi-value type. A record may involve KEY in multiple GIN indexes. So if index is merged in real time when writing, IO will increase sharply and RT will increase in ...
Added by hatching on Wed, 15 May 2019 09:30:25 +0300
We've already talked about it Principle and algorithm of MySQL InnoDB index Here's how to manage and use B+tree indexes and some new features.
Management of B+Tree Index
The basic indexes we use in the InnoDB engine are B+tree indexes.
Create and delete indexes
It can be created and deleted in two ways:
# Mode 1: alter table, in which case bot ...
Added by ehhwan on Wed, 15 May 2019 05:12:03 +0300