NULL en Firebird 6 MiTabla ID Nombre Sueldo 1 Juan 37 2 Perico 3 Andrés 5 4 Roberto 12 5 Antonio ...la sentencia select sum(Sueldo) from MiTabla devuelve 54, que es 37+5+12. Si sumáramos

last_name ------------+----------- iteblog | Hadoop Wu | null Zhang | San (3 rows) cqlsh:iteblog_keyspace> SELECT * FROM iteblog_user WHERE first_name='iteblog'; iteblog_user; first_name | last_name ------------+----------- Wu | Shi Zhang | San (2 rows) 可以看见，key 为 Wu 的数据对应的 last_name 已经有值了。 如果我们使用 UPDATE 命令往表里面更新不存在的数据会发生什么呢？答案是会插入新的数据。 iteblog_user; first_name | last_name ------------+----------- Wu | Shi Zhang | San (2 rows) cqlsh:iteblog_keyspace> UPDATE iteblog_user SET last_name = 'Si' WHERE first_name = 'Li';

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); Note that all data types use rather obvious input formats Language The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish

With Rows The INSERT statement is used to populate a table with rows: INSERT INTO weather VALUES (’San Francisco’, 46, 50, 0.25, ’1994-11-27’); 7 Chapter 2. The SQL Language Note that all data types The point type requires a coordinate pair as input, as shown here: INSERT INTO cities VALUES (’San Francisco’, ’(-194.0, 53.0)’); The syntax used so far requires you to remember the order of the columns to list the columns explicitly: INSERT INTO weather (city, temp_lo, temp_hi, prcp, date) VALUES (’San Francisco’, 43, 57, 0.0, ’1994-11-29’); You can list the columns in a different order if you wish