Python SQLite3数据库日期与时间常见函数用法分析

import sqlite3
#con = sqlite3.connect('example.db')
con = sqlite3.connect(":memory:")
c = con.cursor()
# Create table
c.execute('''CREATE TABLE stocks
       (date text, trans text, symbol text, qty real, price real)''')
# Insert a row of data
c.execute("INSERT INTO stocks VALUES (?,?,?,?,?)", ('2006-03-27','BUY','RHAT',100,60.14))
# Larger example that inserts many records at a time
purchases = [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
       ('2006-04-05', 'BUY', 'MSFT', 1000, 72.00),
       ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
       ('2006-04-07', 'SELL', 'MSFT', 500, 74.00),
       ('2006-04-08', 'SELL', 'IBM', 500, 54.00),
       ('2006-04-09', 'SELL', 'MSFT', 500, 73.00),
       ('2006-04-10', 'SELL', 'MSFT', 500, 75.00),
       ('2006-04-12', 'SELL', 'IBM', 500, 55.00),
      ]
c.executemany('INSERT INTO stocks VALUES (?,?,?,?,?)', purchases)
# Save (commit) the changes
con.commit()
# Do this instead
t = ('RHAT',)
c.execute('SELECT * FROM stocks WHERE symbol=?', t)
#print(c.fetchone())
#for row in c.execute('SELECT * FROM stocks ORDER BY price'):
#  print(row)
#for row in c.execute('SELECT * FROM stocks LIMIT 5 OFFSET 0'):
#  print(row)
for row in c.execute('SELECT * FROM stocks LIMIT 5 OFFSET 1'):
  print(row)
#Select Top N * From
# ====================================================================================
# SQLite 日期 & 时间
# ====================================================================================
print('='*30)
print('SQLite 日期 & 时间')
print('='*30)
# 计算当前日期
c.execute("SELECT date('now')")
print(c.fetchone())
# 计算当前月份的最后一天：
c.execute("SELECT date('now','start of month','+1 month','-1 day');")
print(c.fetchone())
# 计算给定 UNIX 时间戳 1092941466 的日期和时间：
c.execute("SELECT datetime(1092941466, 'unixepoch');")
print(c.fetchone())
# 计算给定 UNIX 时间戳 1092941466 相对本地时区的日期和时间：
c.execute("SELECT datetime(1092941466, 'unixepoch', 'localtime');")
print(c.fetchone())
# 计算当前的 UNIX 时间戳：
c.execute("SELECT datetime(1092941466, 'unixepoch', 'localtime');")
print(c.fetchone())
# 计算美国"独立宣言"签署以来的天数：
c.execute("SELECT julianday('now') - julianday('1776-07-04');")
print(c.fetchone())
# 计算从 2004 年某一特定时刻以来的秒数：
c.execute("SELECT strftime('%s','now') - strftime('%s','2004-01-01 02:34:56');")
print(c.fetchone())
# 计算当年 10 月的第一个星期二的日期：
c.execute("SELECT date('now','start of year','+9 months','weekday 2');")
print(c.fetchone())
# 计算从 UNIX 纪元算起的以秒为单位的时间（类似 strftime('%s','now') ，不同的是这里有包括小数部分）：
c.execute("SELECT (julianday('now') - 2440587.5)*86400.0;")
print(c.fetchone())
# 在 UTC 与本地时间值之间进行转换，当格式化日期时，使用 utc 或 localtime 修饰符，如下所示：
c.execute("SELECT time('12:00', 'localtime');")
print(c.fetchone())
#
c.execute("SELECT time('12:00', 'utc');")
print(c.fetchone())
con.close()
# ====================================================================================
# SQLite 常用函数
# ====================================================================================
print('='*30)
print('SQLite 常用函数')
print('='*30)
con = sqlite3.connect(":memory:")
c = con.cursor()
# Create table
c.execute('''CREATE TABLE COMPANY
      (ID integer, NAME text, AGE integer, ADDRESS text, SALARY real)''')
# Larger example that inserts many records at a time
purchases = [(1,'Paul',32,'California',20000.0),
       (2,'Allen',25,'Texas',15000.0),
       (3,'Teddy',23,'Norway',20000.0),
       (4,'Mark',25,'Rich-Mond',65000.0),
       (5,'David',27,'Texas',85000.0),
       (6,'Kim',22,'South-Hall',45000.0),
       (7,'James',24,'Houston',10000.0)]
c.executemany('INSERT INTO COMPANY VALUES (?,?,?,?,?)', purchases)
# Save (commit) the changes
con.commit()
# 返回数据库表最后 n 行记录
# 先计算一个数据库表中的行数
c.execute("SELECT count(*) FROM COMPANY;")
last = c.fetchone()[0]
n = 5
c.execute("SELECT * FROM COMPANY LIMIT ? OFFSET ?;", (n, last-n))
for row in c:
  print(row)
# 计算一个数据库表中的行数
c.execute("SELECT count(*) FROM COMPANY;")
print(c.fetchone())
# 选择某列的最大值
c.execute("SELECT max(salary) FROM COMPANY;")
print(c.fetchone())
# 选择某列的最小值
c.execute("SELECT min(salary) FROM COMPANY;")
print(c.fetchone())
# 计算某列的平均值
c.execute("SELECT avg(salary) FROM COMPANY;")
print(c.fetchone())
# 为一个数值列计算总和
c.execute("SELECT sum(salary) FROM COMPANY;")
print(c.fetchone())
# 返回一个介于 -9223372036854775808 和 +9223372036854775807 之间的伪随机整数
c.execute("SELECT random() AS Random;")
print(c.fetchone())
# 返回数值参数的绝对值
c.execute("SELECT abs(5), abs(-15), abs(NULL), abs(0), abs('ABC');")
print(c.fetchone())
# 把字符串转换为大写字母
c.execute("SELECT upper(name) FROM COMPANY;")
print(c.fetchone())
# 把字符串转换为小写字母
c.execute("SELECT lower(name) FROM COMPANY;")
print(c.fetchone())
# 返回字符串的长度
c.execute("SELECT name, length(name) FROM COMPANY;")
print(c.fetchone())
# 返回 SQLite 库的版本
c.execute("SELECT sqlite_version() AS 'SQLite Version';")
print(c.fetchone())
#
c.execute("SELECT CURRENT_TIMESTAMP;")
print(c.fetchone())