The Summary of day 3's videos
video 1: the Introduction of SQL
1.SQL is the prominent platform, recent days, SQL is supported by all major commercial database systems.
2.SQL has thousands pages rule users need to follow.
3. SQL can be used interactively with graphical user's interface or just a prompt.
4.SQL is declarative which means you will write some pretty easy queries which say exactly what you want to get data out of the database without describing the process about how to do that picking steps.
in the key point 4, professor in the video introduce the extra thing about the declarative of SQL which called query optimizer. Literately, it optimize the commend in the SQL in the most efficient and fastest way to run
5.languages:
first part: Data Definition Language, the most common use in the language is creating the table in SQL
second part: Data manipulation Language, it allows us using some queries to manipulate the databases.
6.several statements : From clauses, Where clauses , Select clauses.
video 2: the basic features for select statement
1. the definition of select statement is selects the set of attributes from a set of relations satisfying some particular conditions.
2. in the select statement, we have three features: Select, From,Where. Select like Phi in relational Algebra, From means from which relation and where is the specific conditions to filter the data.
3.using join condition can help us combine two tables together with condition, which alway automatically happened with natural join in relational algebra.
4.write down "distinct" after "select "can help us eliminate the duplicates.
5.about the error, when we select a particular attribute in each relations, we absolutely need to distinguish which one it is.
6.order function: we could use order statement to arrangement the data .
7like '%sth%' is a simple way to find some word in your data.
8. we can input * in the first row to point out we need all attributes in the relations.