I am trying to write a table from R to mySQL using dbWriteTable. I would also like to specify that the certain fieldtypes cannot be null and a default value for those specific fieldtypes.
I am currently using the below code to specify the field type but not sure how to specify a default and mark certain fields as cannot be null.
I am trying to preserve the structure of the table as I read it in R. While writing back to sql some elements of the structure are lost.
dbWriteTable(conn = connection,
name = "barcode_details",
value = barcode_details_update,
field.types = c(
id = "float",
order_no = "varchar(50)"))
Related
I imported a CSV file using LOAD DATA INFILE and have this column called Context.
The entire column appears empty - which it shouldn't be, because I already set the DEFAULT to be NULL. So I expected NULL to appear in the entire column.
I have tried if it is empty or NULL but the code below returns 0
SELECT COUNT(*) FROM table
WHERE Context IS NULL OR Context = '';
So now I do not know where the problem is.
FYI: This column is in TEXT datatype and I could change it to VARCHAR, but NOT INT - I don't know if it's related to the problem.
You can manipulate the empty values while importing the data using the SET col_name={expr | DEFAULT}, ... statement while importing the data combined with the function NULLIF(expr1,expr2).
So your query may looks like this:
LOAD DATA INFILE 'file.txt'
INTO table t1
(column1, #var1)
SET Context = NULLIF(#var1, '');
Or you can manipulate all records after the import
UPDATE `table` SET Context2 = NULL WHERE Context2 IS NULL;
LOAD DATA
NULLIF
Based on this thread, I modified my query to the following and was able to solve the problem.
UPDATE table SET Context = NULLIF(Context,' ');
UPDATE table SET Context = NULLIF(Context, '\t');
UPDATE table SET Context = NULLIF(Context, '\n');
UPDATE table SET Context = NULLIF(Context, '\r');
So the original problem could be caused by either \t , \n or \r.
I'm new to SQL, currently I'm doing a task about join two datasets, one of the dataset was created by myself, here's the query I used:
USE `abcde`;
CREATE TABLE `test_01`(
`ID` varchar(50) CHARACTER SET latin1 COLLATE latin1_bin DEFAULT NULL,
`NUMBER01` bigint(20) NOT NULL DEFAULT '0',
`NUMBER02` bigint(20) NOT NULL,
`date01` date DEFAULT NULL,
PRIMARY KEY (`ID`, `date01`))
Then I load the data from a csv file to this table, the csv file looks like this:
ID NUMBER01 NUMBER02 DATE01
aaa=ee 12345678 235896578 **2009-01-01T00:00:00**
If I query this newly-created table, it looks like this(the format of the 'DATE01' changes):
ID NUMBER01 NUMBER02 DATE01
aaa=ee 12345678 235896578 **2009-01-01**
Another dataset, I queried and exported to a csv file, the format of the date01 column is like 01/12/1979 and in SQL the format looks like 1979-12-01.
I also usedselect * from information_schema.columns to check the datatype of the columns I need to join, for the newly-created dataset:
The date column for another dataset is:
The differences are:
1. The format of the date column in csv appears different
2. The COLUMN_DEFAULT are different, one is 0000-00-00, another one is NULL.
I wonder the reason why I got empty output is probably because the difference in the 'date' format, but I'm not sure how to make them the same so that I can get something in the output, can someone gave me some hint? Thank you.
the format of the 'DATE01' changes
Of course, DATE datatype does not contain timezone info/component.
I wonder the reason why I got empty output is probably because the difference in the 'date' format
If input value have some disadvantage (like wrong data format) than according value is truncated or is set to NULL. See - you must obtain a bunch of warnings during the importing similar to "truncate incorrect value".
If the date field in CSV have wrong format then you must use intermediate user-defined variable for accepting raw value, and apply proper converting expression to it in SET clause. Like
LOAD DATA INFILE ...
INTO TABLE tablename (field1, ..., #date01)
SET date01 = STR_TO_DATE(#date01, '%d/%m/%Y');
I'm using MySQL 8 with InnoDB with a node server with mysql2 driver.
My table looks like:
CREATE TABLE IF NOT EXISTS users(
id VARCHAR(36) NOT NULL,
name VARCHAR(32) NOT NULL,
email VARCHAR(255) NOT NULL,
...
PRIMARY KEY (id)
)
I use no auto increment and as VARCHAR ids, I use time based UUIDs.
If I now do my SELECT query:
SELECT * FROM users where id = 'some valid id';
I get my expected result.
If I do:
SELECT * FROM users where id = '0';
I get nothing, because no id in my table has the value '0'.
BUT, if i do:
SELECT * FROM users where id = 0;
I get the last inserted row, which has, of course, a valid VARCHAR id different from 0.
This behavior occured on my node server by accident, because JS sometimes interpretes undefined as 0 in http querys.
In consequence I can easyly avoid inserting 0 in my querys (what I do now), but I would like to understand why this happens.
Your id is varchar(), so this comparison:
WHERE id = 0
requires type conversion.
According to the conversion rules in SQL, the id is turned into a string. Now, in many databases, you would get an error if any values of id could not be converted into numbers.
However, MySQL supports implicit conversion with no errors. (You can read about such conversion in the documentation.) This converts all leading digits to a number -- ignoring the rest. If there are no leading digits, then the value is zero. So, all these are true in MySQL:
'a' = 0
'0a' = 0'
'anything but 0!' = 0
There are two morals to this story.
If you really want id to be a number, then use a number data type (int, bigint, decimal).
Don't mix types in comparisons.
I have the following issue. I have a table called titles with the following structure:
id int(10),
name varchar(100),
At some point later we added a new column called modified_name. It is defined as the same as name except that it is lower case and has all of the spaces replaced with a -. We added this column and so we needed to now get the right modified name value into each record of that column. To do this we wrote a PHP script that handled that by loading in values from the database and processing them, but that is highly inefficient. Is it possible to write a single UPDATE query that would add the correct value to each record in the titles table. I can think of ways to do this with a stored procedure and a while loop there in, but I want to know if something more efficient is possible. It there any way to achieve something like the following:
UPDATE `titles`
SET
`modified_name` = LOWER(REPLACE(SELECT `name` FROM `titles` WHERE id = PRESENT_VALUE), ' ', '-');
The goal being to SET the modified_title column of every record in the titles table to a unique value that results from that record's name column as followed:
# Before modification update query
name = "Hello Goodbye"
modified_name = ""
# After modification update
name = "Hello Goodbye"
modified_name = "hello-goodbye"
Thank you for your help, any advice on how best to do this would be appreciated.
UPDATE `titles` SET `modified_name` = LOWER(REPLACE(`name`, ' ', '-'))
Is there a way in mysql I can set to default?
$q = $dbc -> prepare("UPDATE accounts SET thisColumn = thisColumn(DEFAULT) WHERE id = ?");
Is there a function to set to default in mysql?
There is the DEFAULT keyword:
Use the keyword DEFAULT to set a column explicitly to its default value. This makes it easier to write INSERT statements that assign values to all but a few columns, because it enables you to avoid writing an incomplete VALUES list that does not include a value for each column in the table. Otherwise, you would have to write out the list of column names corresponding to each value in the VALUES list.
You can also use DEFAULT(col_name) as a more general form that can be used in expressions to produce a given column's default value.
DEFAULT(col_name) can only be used if a default is explicitly set for that column, but DEFAULT should always work.
Untested, but this should work:
UPDATE accounts SET thisColumn = DEFAULT WHERE id = ?