Returns the value most recently obtained by the nextval() function. ![]() If FALSE then nextval() will return the specified value, if TRUE then nextval() will increment the specified value and return it. The first parameter is the sequence name, the second parameter is the value to be set as the current value, and the third parameter is a Boolean value TRUE or FALSE. If the sequence is created with the default parameters, then the nextval() will return successive values beginning with 1. Increase the sequence value to its next value and returns that value automatically, even if multiple sessions execute nextval concurrently. OWNED BY: Allows you to associate the column of a table with a sequence, so that when you drop the column or table, PostgreSQL will drop the associated sequence automatically. PostgreSQL pre-allocates the number of sequence numbers specified by the CACHE. Cycling will restart the sequence from the minimum or maximum value and not from the start value.ĬACHE : Improves performance for applications using sequence objects by minimizing the number of disk IOs that are required to generate sequence numbers. It defaults to the maximum value of the data type of the sequence.ĬYCLE: Specifies whether the sequence object should restart from the minimum value (maximum value for descending sequence) or raise an exception when the minimum (or maximum) value is reached. MAXVALUE: Specify the upper bound for the sequence. If not specified, it defaults to the minimum value of the data type of the sequence. MINVALUE: This specifies the lower bound for a sequence. If the increment value is negative, then the sequence is a decreasing sequence else it is ascending. Increment_value: This is the interval between two consecutive sequence values. Start_value: The first value in the sequence. Integer_type: A sequence is defined with any of the integer types as INT, SMALLINT, BIGINT, and NUMERIC data type. The sequence_name is the unique name of a sequence that you want to create. If a sequence already exists, Postgres will only give a warning instead of an error and skip creating a new sequence. Theoretical and Applied Genetics, 85: 985-993.After CREATE SEQUENCE you can specify the optional IF NOT EXISTS clause, which will create a sequence only if it does not exist. WeaknessesDisadvantages include the need for sequence data to design the PCR primers.ĪpplicationsSCARs are locus specific and have been applied in gene mapping studies and marker assisted selection.ĭevelopment of reliable PCR based markers linked to downy mildew resistance genes in lettuce Paran, I. ![]() Due to the use of PCR, only low quantities of template DNA are required. In addition, SCARs have a high reproducibility and are locus-specific. StrengthsThe main advantage of SCARs is that they are quick and easy to use. ![]() Length polymorphisms are detected by gel electrophoresis. Obtaining a codominant marker may be an additional advantage of converting RAPDs into SCARs, although SCARs may exhibit dominance when one or both primers partially overlap the site of sequence variation. By using longer PCR primers, SCARs do not face the problem of low reproducibility generally encountered with RAPDs. DescriptionSCARs are DNA fragments amplified by the PCR using specific 15-30 bp primers, designed from nucleotide sequences established from cloned RAPD fragments linked to a trait of interest.
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