SQLite3中的日期时间函数使用小结

import sqlite3
conn = sqlite3.connect('/tmp/sqlite.db')
cur = conn.cursor()

create_table_stmt = '''CREATE TABLE IF NOT EXISTS test_table (
 id INTEGER PRIMARY KEY AUTOINCREMENT,
 duration INTEGER,
 event_date TEXT,
 parameter TEXT );'''

create_index = 'CREATE INDEX IF NOT EXISTS idx_id ON test_table (id);'
cur.execute(create_table_stmt)
cur.execute(create_index)
conn.commit()

NULL. The value is a NULL value    
INTEGER. The value is a signed integer, stored in 1, 2, 3, 4, 6, or 8 bytes depending on the magnitude of the value
REAL. The value is a floating point value, stored as an 8-byte IEEE floating point number
TEXT. The value is a text string, stored using the database encoding (UTF-8, UTF-16BE or UTF-16LE)
BLOB. The value is a blob of data, stored exactly as it was input

TEXT as ISO8601 strings ('YYYY-MM-DD HH:MM:SS.SSS').
REAL as Julian day numbers, the number of days since noon in Greenwich on November 24, 4714 B.C. according to the proleptic Gregorian calendar.
INTEGER as Unix Time, the number of seconds since 1970-01-01 00:00:00 UTC.

insert_stmt = 'insert into test_table values (?, ?, ?)'
record = (123, '2011-11-30 12:34:56', 'hello world')
cur.execute( insert_stmt, record )
conn.commit()

SELECT
 id,
 duration,
 event_date,
 parameter
 FROM test_table
WHERE
 DATE(event_date) = DATE('now', '-1 day', 'localtime')
ORDER BY id, event_date

datetime() .......................  产生日期和时间
date()  ........................... 产生日期
time()  ........................... 产生时间
strftime() .......................  对以上三个函数产生的日期和时间进行格式化

YYYY-MM-DD
YYYY-MM-DD HH:MM
YYYY-MM-DD HH:MM:SS
HH:MM
HH:MM:SS
now                                 # 其中now是产生现在的时间。

select datetime('now');
结果：2006-10-17 12:55:54

select datetime('2006-10-17');
结果：2006-10-17 12:00:00

select datetime('2006-10-17 00:20:00', '+1 hour', '-12 minute');
结果：2006-10-17 01:08:00

select date('2006-10-17', '+1 day', '+1 year');
结果：2007-10-18

select datetime('now', 'start of year');
结果：2006-01-01 00:00:00

select datetime('now', 'start of month');
结果：2006-10-01 00:00:00

select datetime('now', 'start of day');
结果：2006-10-17 00:00:00

# 尽管第2个参数加上了10个小时，但是却被第3个参数 start of day 把时间归零到00:00:00
# 随后的第4个参数在00:00:00的基础上把时间增加了10个小时变成了10:00:00。
select datetime('now', '+10 hour', 'start of day', '+10 hour');
结果：2006-10-17 10:00:00

# 把格林威治时区转换成本地时区。
select datetime('now', 'localtime');
结果：2006-10-17 21:21:47

select datetime('now', '+8 hour');
结果：2006-10-17 21:24:45

select strftime('%Y/%m/%d %H:%M:%S', 'now', 'localtime');