In mysql you can view a table's structure via explain tablename; What is the equivalent for sqlite3?
I believe ".schema tablename" is what you're looking for.
You can use .schema in the Command Line Shell:
With no arguments, the ".schema"
command shows the original CREATE
TABLE and CREATE INDEX statements that
were used to build the current
database. If you give the name of a
table to ".schema", it shows the
original CREATE statement used to make
that table and all if its indices.
This was already answered in a more generic way here.
Edit:
Note that .schema will also give you INDEXES that match the same name.
Example:
CREATE TABLE job (
id INTEGER PRIMARY KEY,
data VARCHAR
);
CREATE TABLE job_name (
id INTEGER PRIMARY KEY,
name VARCHAR
);
CREATE INDEX job_idx on job(data);
Note the differences between:
sqlite> SELECT sql FROM SQLITE_MASTER WHERE type = 'table' AND name = 'job';
CREATE TABLE job (
id INTEGER PRIMARY KEY,
data VARCHAR
)
sqlite> SELECT sql FROM SQLITE_MASTER WHERE name = 'job_idx';
CREATE INDEX job_idx on job(data)
and
sqlite> .schema job
CREATE TABLE job (
id INTEGER PRIMARY KEY,
data VARCHAR
);
CREATE INDEX job_idx on job(data);
Including the semi-colon at the end of the queries.
Related
I have a primary key column in my SQL table in PostgreSQL named "id". It is a "bigseries" column. I want to convert the column to a "UUID" column. It entered the below command in the terminal:
alter table people alter column id uuid;
and
alter table people alter column id uuid using (uuid_generate_v4());
but neither of them worked.
In both tries I got the error message
ERROR: syntax error at or near "uuid"
LINE 1: alter table people alter column id uuid using (uuid_generate...
What is the correct syntax?
First of all uuid_generate_v4() is a function which is provided by an extension called uuid-ossp. You should have install that extension by using;
CREATE EXTENSION uuid-ossp;
Postgresql 13 introduced a new function which does basically the same without installing extension. The function is called gen_random_uuid()
Suppose that we have a table like the one below;
CREATE TABLE people (
id bigserial primary key,
data text
);
The bigserial is not a real type. It's a macro which basically creates bigint column with default value and a sequence. The default value is next value of that sequence.
For your use case, to change data type, you first should drop the old default value. Then, alter the type and finally add new default value expression. Here is the sample:
ALTER TABLE people
ALTER id DROP DEFAULT,
ALTER id TYPE uuid using (gen_random_uuid() /* or uuid_generate_v4() */ ),
ALTER id SET DEFAULT gen_random_uuid() /* or uuid_generate_v4() */ ;
CREATE TABLE IF NOT EXISTS people (
id uuid NOT NULL CONSTRAINT people_pkey PRIMARY KEY,
address varchar,
city varchar(255),
country varchar(255),
email varchar(255),
phone varchar(255)
);
This is the correct syntax to create table in postgres SQL, it's better to do these constraints at beginning to avoid any error.
For using alter command you would do the following:
ALTER TABLE customer ADD COLUMN cid uuid PRIMARY KEY;
Most of errors that you could find while writing command either lower case or undefined correct the table name or column.
In Postgres, defining a column with SERIAL/BIGSERIAL has a triple effect as discussed here:
Define a int/bigint column.
Create a sequence object to generate auto-incrementing numbers.
Set the default of the column to call nextval() on the sequence.
Is there a similar shortcut command in H2 to get this related set of behavior?
If not, what would the long version of the SQL be?
Where does the sequence live? How can you adjust its value or reset it?
If you create a column as auto_increment (or identity) H2 creates a sequence in the background. The name of that sequence can be obtained by looking at information_schema.columns:
create table foo
(
id integer auto_increment,
other_column varchar(20)
);
If you then run:
select column_name, column_default
from information_schema.columns
where table_name = 'FOO'
and table_schema = 'PUBLIC';
You'll get something like this:
COLUMN_NAME | COLUMN_DEFAULT
-------------+-----------------------------------------------------------------------------
ID | (NEXT VALUE FOR PUBLIC.SYSTEM_SEQUENCE_C1C36118_ED1C_44D6_B573_6C00C5923EAC)
OTHER_COLUMN |
You can alter that sequence without problems:
alter sequence SYSTEM_SEQUENCE_C1C36118_ED1C_44D6_B573_6C00C5923EAC
restart with 42;
This is essentially identical to Postgres' serial data type
If not, what would the long version of the SQL be?
create sequence foo_id_seq;
create table foo
(
id integer default foo_id_seq.nextval,
other_column varchar(20)
);
The big difference between this and a Postgres serial is that H2 does not know that the sequence "belongs" to the column. You need to drop it manually when the table is dropped.
foo_id_seq.nextval will actually be converted to (NEXT VALUE FOR PUBLIC.FOO_ID_SEQ) when the table is created (and it will be stored like that in information_schema.columns.
I am trying to create table having different indexes with single query but H2 gives Error for example:
create table tbl_Cust
(
id int primary key auto_increment not null,
fid int,
c_name varchar(50),
INDEX (fid)
);
but this gives error as
Unknown data type: "("; SQL statement:
[Error Code: 50004]
[SQL State: HY004]
Due to this I have to run 2 different queries to create table with Index. First query to create table and then second query to add index with
create INDEX c_fid on tbl_Cust(fid);
Is there something wrong in my query or H2 simply does not support this creation of table with index in single query?
Interesting question. The solution is even more interesting, as it involves MySQL compatibility mode.
It's actually possible to perform the exact same command you wrote without any modification, provided you just add to your jdbc url the MySQL mode.
Example URL like this: jdbc:h2:mem:;mode=mysql
SQL remains:
create table tbl_Cust
(
id int primary key auto_increment not null,
fid int,
c_name varchar(50),
INDEX (fid)
);
Update count: 0
(15 ms)
Too bad I did not see this question earlier... Hopefully the solution might become handy one day to someone :-)
I could resolve the problem. According to
http://www.h2database.com/html/grammar.html#create_index
I modified the query. It works fine with my H2 server.
CREATE TABLE subscription_validator (
application_id int(11) NOT NULL,
api_id int(11) NOT NULL,
validator_id int(11) NOT NULL,
PRIMARY KEY (application_id,api_id),
CONSTRAINT subscription_validator_ibfk_1 FOREIGN KEY (validator_id) REFERENCES validator (id) ON UPDATE CASCADE
);
CREATE INDEX validator_id ON subscription_validator(validator_id);
I have 3 Questions
1) Can Adobe Air Database create more than 1 table in the DB?
will it work by just executing two create table statement work?
sqls.sqlConnection = sqlc;
sqls.text = "Create table if not exists test_table ( id INTEGER PRIMARY KEY autoincrement, first_name TEXT, last_name TEXT);"
sqls.execute();
sqls.text = "Create table if not exists test_table2 ( id INTEGER PRIMARY KEY autoincrement, first_name TEXT, last_name TEXT);";
sqls.execute();
2) How can i do SQL indexing for a table in a database?
sqls.text= "create index index_1 ON test_table (first_name);";
sqls.execute();
Will this work for indexing?
3) If all the above work, how to i check if the database is implementing the above?
1) Yes.
2) Yes. http://www.sqlite.org/lang_createindex.html I'm not sure if this is what you want, but you can force the use of an index in SQLite via the INDEXED BY keyword: http://www.sqlite.org/lang_indexedby.html
Okay no seriously, if a PostgreSQL guru can help out I'm just getting started.
Basically what I want is a simple table like such:
CREATE TABLE schema.searches
(
search_id serial NOT NULL,
search_query character varying(255),
search_count integer DEFAULT 1,
CONSTRAINT pkey_search_id PRIMARY KEY (search_id)
)
WITH (
OIDS=FALSE
);
I need something like REPLACE INTO for MySQL. I don't know if I have to write my own procedure or something?
Basically:
check if the query already exists
if so, just add 1 to the count
it not, add it to the db
I can do this in my php code but I'd rather all that be done in postgres C engine
You have to add a unique constraint first.
ALTER TABLE schema.searches ADD UNIQUE (search_query);
The insert/replace command looks like this.
INSERT INTO schema.searches(search_query) VALUES ('a search query')
ON CONFLICT (search_query)
DO UPDATE SET search_count = schema.searches.search_count + 1;