4.创建表格

检查表格式否存在：

SELECT EXISTS (SELECT relname FROM pg_class WHERE relname =
‘{tablename}’);

You can create a new table by specifying the table name, along with all
column names and their types:

CREATE TABLE weather (

city varchar(80),

temp_lo int, – low temperature

temp_hi int, – high temperature

prcp real, – precipitation

date date

);

You can enter this into psql with the line breaks. psql will recognize
that the command is not terminated until the semicolon.

White space (i.e., spaces, tabs, and newlines) can be used freely in SQL
commands. That means you can type the command aligned differently than
above, or even all on one line. Two dashes (“–”) introduce comments.
Whatever follows them is ignored up to the end of the line. SQL is case
insensitive about key words and identifiers, except when identifiers are
double-quoted to preserve the case (not done above).

varchar(80) specifies a data type that can store arbitrary character
strings up to 80 characters in length. int is the normal integer
type. real is a type for storing single precision floating-point
numbers. date should be self-explanatory. (Yes, the column of
type date is also named date. This might be convenient or confusing —
you choose.)

PostgreSQL supports the standard SQL types int, smallint, real, double
precision, char(N), varchar(N), date, time, timestamp,
and interval, as well as other types of general utility and a rich set
of geometric types. PostgreSQL can be customized with an arbitrary
number of user-defined data types. Consequently, type names are not key
words in the syntax, except where required to support special cases in
the SQL standard.

The second example will store cities and their associated geographical
location:

CREATE TABLE cities (

name varchar(80),

location point

);

The point type is an example of a PostgreSQL-specific data type.

Finally, it should be mentioned that if you don’t need a table any
longer or want to recreate it differently you can remove it using the
following command:

DROP TABLE tablename;