DROP 명령과 CASCADE·RESTRICT 문서의 검증 코드다. if __name__ == "__main__": 아래가 자체 테스트다.
# 58.DROP 명령과 CASCADE·RESTRICT 검증 (표준 라이브러리 sqlite3만 쓴다. 실행: python3 58_sql-drop_verify.py)
# 확인하는 것 ("DELETE는 행만, DROP TABLE은 표의 정의까지")
# 1. DELETE FROM DEPENDENT 뒤에는 표가 남아 다시 넣을 수 있다
# 2. DROP TABLE DEPENDENT 뒤에는 표 자체가 없어 넣을 수도 찾을 수도 없다
# 3. SQLite에는 DROP SCHEMA와 DROP의 CASCADE·RESTRICT가 없다
# CASCADE와 RESTRICT가 실제로 하는 일은 PostgreSQL에서 확인했다(58_sql-drop_verify.sql).
import sqlite3
# COMPANY 스키마와 상태.
# 손본 곳은 둘이다. (1) EMPLOYEE의 외래 키 두 개를 CREATE TABLE 안에 적었다(SQLite는 아직 없는
# 표를 가리켜도 받는다). (2) WORKS_ON.Hours의 NOT NULL은 뺐다(상태에 Hours가 NULL인 행이 있다).
COMPANY_DDL = """
CREATE TABLE EMPLOYEE (
Fname VARCHAR(15) NOT NULL, Minit CHAR, Lname VARCHAR(15) NOT NULL, Ssn CHAR(9) NOT NULL,
Bdate DATE, Address VARCHAR(30), Sex CHAR, Salary DECIMAL(10,2), Super_ssn CHAR(9), Dno INT NOT NULL,
PRIMARY KEY (Ssn),
FOREIGN KEY (Super_ssn) REFERENCES EMPLOYEE(Ssn),
FOREIGN KEY (Dno) REFERENCES DEPARTMENT(Dnumber));
CREATE TABLE DEPARTMENT (
Dname VARCHAR(15) NOT NULL, Dnumber INT NOT NULL, Mgr_ssn CHAR(9) NOT NULL, Mgr_start_date DATE,
PRIMARY KEY (Dnumber), UNIQUE (Dname),
FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE(Ssn));
CREATE TABLE DEPT_LOCATIONS (
Dnumber INT NOT NULL, Dlocation VARCHAR(15) NOT NULL,
PRIMARY KEY (Dnumber, Dlocation),
FOREIGN KEY (Dnumber) REFERENCES DEPARTMENT(Dnumber));
CREATE TABLE PROJECT (
Pname VARCHAR(15) NOT NULL, Pnumber INT NOT NULL, Plocation VARCHAR(15), Dnum INT NOT NULL,
PRIMARY KEY (Pnumber), UNIQUE (Pname),
FOREIGN KEY (Dnum) REFERENCES DEPARTMENT(Dnumber));
CREATE TABLE WORKS_ON (
Essn CHAR(9) NOT NULL, Pno INT NOT NULL, Hours DECIMAL(3,1),
PRIMARY KEY (Essn, Pno),
FOREIGN KEY (Essn) REFERENCES EMPLOYEE(Ssn),
FOREIGN KEY (Pno) REFERENCES PROJECT(Pnumber));
CREATE TABLE DEPENDENT (
Essn CHAR(9) NOT NULL, Dependent_name VARCHAR(15) NOT NULL, Sex CHAR, Bdate DATE, Relationship VARCHAR(8),
PRIMARY KEY (Essn, Dependent_name),
FOREIGN KEY (Essn) REFERENCES EMPLOYEE(Ssn));
"""
EMPLOYEE = [
('John', 'B', 'Smith', '123456789', '1965-01-09', '731 Fondren, Houston, TX', 'M', 30000, '333445555', 5),
('Franklin', 'T', 'Wong', '333445555', '1955-12-08', '638 Voss, Houston, TX', 'M', 40000, '888665555', 5),
('Alicia', 'J', 'Zelaya', '999887777', '1968-01-19', '3321 Castle, Spring, TX', 'F', 25000, '987654321', 4),
('Jennifer', 'S', 'Wallace', '987654321', '1941-06-20', '291 Berry, Bellaire, TX', 'F', 43000, '888665555', 4),
('Ramesh', 'K', 'Narayan', '666884444', '1962-09-15', '975 Fire Oak, Humble, TX', 'M', 38000, '333445555', 5),
('Joyce', 'A', 'English', '453453453', '1972-07-31', '5631 Rice, Houston, TX', 'F', 25000, '333445555', 5),
('Ahmad', 'V', 'Jabbar', '987987987', '1969-03-29', '980 Dallas, Houston, TX', 'M', 25000, '987654321', 4),
('James', 'E', 'Borg', '888665555', '1937-11-10', '450 Stone, Houston, TX', 'M', 55000, None, 1)]
DEPARTMENT = [('Research', 5, '333445555', '1988-05-22'), ('Administration', 4, '987654321', '1995-01-01'),
('Headquarters', 1, '888665555', '1981-06-19')]
DEPT_LOCATIONS = [(1, 'Houston'), (4, 'Stafford'), (5, 'Bellaire'), (5, 'Sugarland'), (5, 'Houston')]
PROJECT = [('ProductX', 1, 'Bellaire', 5), ('ProductY', 2, 'Sugarland', 5), ('ProductZ', 3, 'Houston', 5),
('Computerization', 10, 'Stafford', 4), ('Reorganization', 20, 'Houston', 1), ('Newbenefits', 30, 'Stafford', 4)]
WORKS_ON = [('123456789', 1, 32.5), ('123456789', 2, 7.5), ('666884444', 3, 40.0), ('453453453', 1, 20.0),
('453453453', 2, 20.0), ('333445555', 2, 10.0), ('333445555', 3, 10.0), ('333445555', 10, 10.0),
('333445555', 20, 10.0), ('999887777', 30, 30.0), ('999887777', 10, 10.0), ('987987987', 10, 35.0),
('987987987', 30, 5.0), ('987654321', 30, 20.0), ('987654321', 20, 15.0), ('888665555', 20, None)]
DEPENDENT = [('333445555', 'Alice', 'F', '1986-04-05', 'Daughter'), ('333445555', 'Theodore', 'M', '1983-10-25', 'Son'),
('333445555', 'Joy', 'F', '1958-05-03', 'Spouse'), ('987654321', 'Abner', 'M', '1942-02-28', 'Spouse'),
('123456789', 'Michael', 'M', '1988-01-04', 'Son'), ('123456789', 'Alice', 'F', '1988-12-30', 'Daughter'),
('123456789', 'Elizabeth', 'F', '1967-05-05', 'Spouse')]
def load(c):
"""여섯 표에 COMPANY 상태를 넣는다. EMPLOYEE와 DEPARTMENT가 서로를 가리키므로 넣는 동안만 외래 키 검사를 미룬다."""
c.execute('BEGIN')
c.execute('PRAGMA defer_foreign_keys = ON')
c.executemany('INSERT INTO EMPLOYEE VALUES (?,?,?,?,?,?,?,?,?,?)', EMPLOYEE)
c.executemany('INSERT INTO DEPARTMENT VALUES (?,?,?,?)', DEPARTMENT)
c.executemany('INSERT INTO DEPT_LOCATIONS VALUES (?,?)', DEPT_LOCATIONS)
c.executemany('INSERT INTO PROJECT VALUES (?,?,?,?)', PROJECT)
c.executemany('INSERT INTO WORKS_ON VALUES (?,?,?)', WORKS_ON)
c.executemany('INSERT INTO DEPENDENT VALUES (?,?,?,?,?)', DEPENDENT)
c.execute('COMMIT')
def make(ddl=COMPANY_DDL):
"""외래 키 검사를 켠 메모리 데이터베이스에 COMPANY를 만들어 돌려준다."""
c = sqlite3.connect(':memory:', isolation_level=None)
c.execute('PRAGMA foreign_keys = ON')
c.executescript(ddl)
load(c)
return c
def rows(c, sql, args=()):
return c.execute(sql, args).fetchall()
def error_of(c, sql, args=()):
"""문장을 돌려 보고 오류 글을 돌려준다. 오류가 없으면 None. 어느 쪽이든 데이터베이스는 돌리기 전으로 되돌린다."""
c.execute('SAVEPOINT try_it')
try:
c.execute(sql, args)
return None
except sqlite3.Error as e:
return str(e)
finally:
c.execute('ROLLBACK TO try_it')
c.execute('RELEASE try_it')
def tables(c):
return sorted(r[0] for r in rows(c, "SELECT name FROM sqlite_master WHERE type = 'table'"))
if __name__ == "__main__":
c = make()
assert 'DEPENDENT' in tables(c) and rows(c, "SELECT COUNT(*) FROM DEPENDENT") == [(7,)]
# --- 1. DELETE: 행만 사라진다
c.execute("DELETE FROM DEPENDENT")
assert rows(c, "SELECT COUNT(*) FROM DEPENDENT") == [(0,)]
assert 'DEPENDENT' in tables(c) # 카탈로그에 정의가 남아 있다
assert len(rows(c, "PRAGMA table_info(DEPENDENT)")) == 5 # 열 다섯 개도 그대로
c.execute("INSERT INTO DEPENDENT VALUES ('123456789', 'Michael', 'M', '1988-01-04', 'Son')")
assert rows(c, "SELECT COUNT(*) FROM DEPENDENT") == [(1,)] # 다시 넣을 수 있다
assert error_of(c, "INSERT INTO DEPENDENT VALUES ('000000000', 'Nobody', 'M', NULL, 'Son')") == 'FOREIGN KEY constraint failed' # 제약도 살아 있다
# --- 2. DROP TABLE: 정의까지 사라진다
c.execute("DROP TABLE DEPENDENT")
assert 'DEPENDENT' not in tables(c) and len(tables(c)) == 5
assert error_of(c, "SELECT COUNT(*) FROM DEPENDENT") == 'no such table: DEPENDENT'
assert error_of(c, "INSERT INTO DEPENDENT VALUES ('123456789', 'Michael', 'M', '1988-01-04', 'Son')") == 'no such table: DEPENDENT'
# DELETE는 제약을 지킨다: 다른 표가 가리키는 행은 못 지운다
assert error_of(c, "DELETE FROM PROJECT") == 'FOREIGN KEY constraint failed'
assert rows(c, "SELECT COUNT(*) FROM PROJECT") == [(6,)]
# --- 3. SQLite가 못 받는 문장
c = make()
for sql in ("DROP TABLE DEPENDENT CASCADE", "DROP TABLE DEPENDENT RESTRICT", "DROP SCHEMA COMPANY CASCADE", "DROP SCHEMA COMPANY RESTRICT"):
assert 'syntax error' in error_of(c, sql), sql
assert len(tables(c)) == 6
print('ALL CHECKS PASSED')